Search

Herein, a simple in situ hydrothermal carbonization (HTC) approach has been used to synthesize different ratios of carbon-incorporated nickel cobaltite nanocomposites, denoted as NiCo2O4/C (Dx) (where x = 1, 2, 5, and 10, representing the molar ratio of dextrose to nickel precursor). The prepared nanomaterials were further characterized using XRD, SEM, TEM, Raman, FT-IR, BET, and XPS techniques and subsequently subjected to supercapacitor (SC) studies using 3 M KOH as the electrolyte. In the three-electrode SC studies, NiCo2O4/C (D2) showed a superior specific capacitance of 736 F g−1 at 1 A g−1 in comparison with pure NiCo2O4 (307 F g−1) and carbon nanospheres (CNS, 52 F g−1), with appreciable cycling stability, retaining about 85% of capacity up to 1000 cycles. Furthermore, in the two-electrode SC studies for NiCo2O4/C (D2) at 1 A g−1, the asymmetric configuration exhibited twice the energy density (20.3 W h kg−1) and power density (406 W kg−1) compared to the symmetric configuration, due to the hybrid EDLC–pseudocapacitive mechanism. In contrast, the symmetric configuration showed lower energy density (13.5 W h kg−1) and power density (213 W kg−1) owing to pseudocapacitive behavior alone. This noted synergistic enhancement effect on the supercapacitor performance of the NiCo2O4/C (D2) nanocomposite can be ascribed to the incorporation of optimal carbon content into NiCo2O4 to facilitate more electroactive sites for charge storage compared to pure NiCo2O4 and CNS. This kind of tuning of the carbon ratios in the metal oxide/carbon nanocomposites through the in situ HTC approach and tailoring the symmetric/asymmetric SC device configurations will efficiently deliver a promising SC in the near future. [ABSTRACT FROM AUTHOR]

This study reports the use of deep‐eutectic‐solvent‐ (DES‐) assisted hydrothermal carbonization (HTC) to disrupt the floc structure of sewage sludge (SS) for deep carbonization, with the resulting hydrochars employed in the preparation of formaldehyde‐free plywood bioadhesives. Sewage‐sludge‐based bioadhesive exhibits an excellent wet shear strength, complying with the requirements of Chinese national standard GB/T 9846–2015 (≥0.7 MPa). The molecular weight of proteins and the formation of covalent bonds via dehydration have a notable role in improving adhesive performance (wet shear strength). The Maillard reaction is a key reaction during HTC to destroy the secondary structure of proteins, resulting in the release of more OH and NH2. The main reaction during hot‐press treatment is dehydration. High ash content in bioadhesives improves flame resistance potential, particularly on addition of DES. A plausible mechanism is proposed for this. This work provides a new method for the valorization of SS‐derived hydrochars and contributes to the development of greener formaldehyde‐free wood bioadhesives. [ABSTRACT FROM AUTHOR]

• Advancements in sludge processing to reduce particle and acidification emissions. • Reduced environmental footprint through innovative sludge treatment. • Sludge hydrochar carbon stabilization contributes to climate change mitigation. Proper management of wastewater treatment plant side streams in pulp and paper mills is a matter of great interest. This study evaluates the environmental impact of different strategies in the management of biosludge from pulp and paper mills in Finland through a Life Cycle Assessment methodology. The base industrial standard practice, biosludge incineration for energy recovery and ash landfill disposal (Scenario 1), was compared to the alternative process of hydrothermal carbonization. The hydrochar generated from hydrothermal carbonization was evaluated for energy recovery through incineration (Scenario 2), or for use in composting for nutrient recovery (Scenario 3). The results showed that the hydrothermal process improved the overall environmental performance of the sludge management, particularly in terms of energy consumption and greenhouse gas emissions. The use of hydrochar as a soil amendment in composting also resulted in a significant reduction on the environmental impact compared to the other two scenarios. Overall, this study highlights the potential of hydrothermal carbonization and hydrochar utilization as sustainable options for managing biosludge from pulp mills. [ABSTRACT FROM AUTHOR]

With the growing rise in CO2 emission, resulting in accelerated global warming, there is an increased utilization of lignocellulosic waste biomass to synthesize inexpensive CO2 adsorbents, via hydrothermal carbonization (HTC) of biomass followed by chemical activation (CAC) to create porous activated hydrochar that can capture CO2. However, despite analogous thermochemical conversion (HTC and CAC) conditions, the activated hydrochars derived from different biomass precursors exhibit dissimilarity in surface morphology and its corresponding CO2 capture capacity. Hence, finding the fundamental key underlying this discrepancy is of interest where biopolymer constituents' composition is hypothesized to be the determining factor. This study, therefore, explored the biopolymer model compounds of cellulose, hemicellulose, lignin, and glucose which were independently hydrothermally carbonized and KOH-activated to develop porous adsorbents. The findings of this study highlighted discrete porosity development in the biopolymer-derived activated hydrochar ranging from 591 m2/g for glucose precursor to as high as 2279 m2/g for that cellulose. On the other hand, lignin-based activated hydrochar demonstrated the lowest microporosity (0.084 cm3/g), reflecting its reluctance in transforming the hydrochar carbon matrix into substantially rich micro-cavities, at moderate HTC and CAC conditions. CO2 capture was observed to be the lowest of 1.45 mmol/g for glucose and highest of 2.45 mmol/g for cellulose-derived activated hydrochars, reflecting the direct influence of surface porosity on CO2 adsorbed. Literature data of other lignocellulosic biomass-derived activated hydrochars were combined with results of this study where a statistical analysis revealed the inhibiting role of glucose in pore creation while micropore creation was favored by cellulose and hemicellulose, benefitting CO2 capture. [ABSTRACT FROM AUTHOR]

In this work, various waste biomasses were subjected to hydrothermal carbonization under mild conditions. The effect of operating temperature, duration time, and biomass-to-water ratio on the chemical and combustion characteristics of the hydrochars were determined. The results were compared to MKP Alpagut lignite to understand the future of hydrochars as an effective and environmentally friendly solid fuel. It was found that the temperature dominantly affects the yield and the chemical characteristics of the hydrochars compared to the duration time and biomass-to-water ratio for real biomasses. Hydrochars obtained from real biomasses showed higher combustion temperatures and slightly higher ignition temperatures. Moreover, the HHV of hydrochar is significantly higher than the MKP lignite and raw biomass. Our results prove that the hydrothermal carbonization process can be assessed as one of the best techniques for the thermochemical conversion of waste biomass into high-value-added valuable solid fuels. [ABSTRACT FROM AUTHOR]

Biomass-to-biofuel conversion represents a critical component of the global transition to renewable energy. One of the most accessible types of biomass is sewage sludge (SS). This by-product from wastewater treatment plants (WWTPs) contains microplastics (MPs) originating from household, industrial and urban runoff sources. Due to their small size (<5 mm) and persistence, MPs present a challenge when they are removed from sewage systems, where they mainly accumulate (~90%). The presence of MPs in SS poses environmental risks when biosolids are applied as fertilizer in agriculture or incinerated for the purpose of energy production. The key problem is the efficient and reliable identification and reduction of MPs in sewage systems, due to the lack of standardized procedures. The reduction methods for MPs might involve physical, chemical, biological, and hydrothermal approaches, including hydrothermal carbonization (HTC). The HTC of SS produces hydrochar (HC), a solid biofuel, and presents a cutting-edge approach that simultaneously addresses secondary microplastic pollution and renewable biomass-derived energy production. In this article, we review briefly the MPs content in biosolids from different countries, and present HTC as a promising method for their removal from SS. In conclusion, HTC (i) effectively reduces the abundance of MPs in biosolids, (ii) produces an improved solid source of energy, and (iii) contributes to circular SS management. [ABSTRACT FROM AUTHOR]

The purpose of this research was to develop an integrated biorefinery process of solid-state anaerobic digestion (SS-AD) and hydrothermal carbonization (HTC) for the co-production of methane and hydrochar using elephant dung (ED) as substrate. With a leachate recirculation rate of 4 times/day, the SS-AD presented the highest cumulative methane yield of 83.2 ± 1.7 NmL/g volatile solid (VS)added and VS removal efficiency of 53.9 ± 0.3%. In subsequent HTC, the maximum higher heating value (HHV) of 10,078.5 ± 288.5 MJ/ton dry wt. was achieved for the digested ED without leachate recirculation under HTC temperature of 170 °C. In addition, the maximum mass and energy yields were 76.3 ± 0.8% and 84.1 ± 0.3%, respectively. The produced hydrochar had higher HHV compared to the raw digestate. Moreover, the HHV of the hydrochar was higher, and ash content was identical to conventional coal (lignite). An assessment of a full-scale elephant-sanctuary waste management scheme integrating SS-AD and HTC indicates that more than 10,078.5 ± 288.5 MJ of energy and 563.0 ± 5.2 kg dry weight of hydrochar could be recovered per ton dry weight of ED. The developed elephant dung management platform could enhance energy yield from ED while addressing environmental issues. [ABSTRACT FROM AUTHOR]

The characteristics of biochar vary widely depending on the type of biomass and thermochemical conversion method. In this study, four types of biomass (kenaf, rice husk, corncob, and wood chips) were subjected to hydrothermal carbonization and torrefaction at 220 °C, 260 °C, and 300 °C for 30 min. The acquired biochars showed significant differences in the type of reaction and biomass. At each temperature, the decomposition of volatiles was more severe in hydrochar (HC) than in torrefied char (TC). The mass yields of HC were 44.30–61.63 wt.% (220 °C), 20.89–37.04 wt.% (260 °C), and 12.59–29.19 wt.% (300 °C), whereas the mass yields of TC were 94.73–97.69 wt.% (220 °C), 87.19–95.04 wt.% (260 °C), and 68.22–80.78 wt.% (300 °C). The elemental and thermal characteristics of TC changed gradually as the reaction temperature increased, and the characteristics of HC were enhanced rapidly. Wood chip biochar that was reacted at 300 °C showed the highest heating values of 28.77 MJ/kg (HC) and 21.09 MJ/kg (TC). The results of chemical analyses showed that hydrothermal carbonization strongly affected the cleavage of inter- and intra-molecular carbon bonds in cellulose and hemicellulose. In contrast, torrefaction removed the thermally fragile moisture and hemicellulose content from biomass. [ABSTRACT FROM AUTHOR]

The reuse of heavy-metal hyperaccumulator waste has emerged as a critical constraint in the implementation of phytoremediation to control heavy-metal pollution. Ramie (Boehmeria nivea) is a well-established arsenic (As) hyperaccumulator that has been widely used in the remediation of As-contaminated sites in recent years. To facilitate multipurpose development and the recycling of ramie straw contaminated with heavy metals, a study investigated the preparation of hydrochar (HC) at different temperatures and assessed the feasibility of reintroducing the HC into the soil. The results indicated higher yields, increased nutrient contents, and reduced As percentage levels at a hydrothermal carbonization temperature of 240°C. Treatment with a 300 mmol/L sodium hydroxide solution resulted in the removal of As from HC, ranging from 77.06% to 87.60%, effectively facilitating the reuse of HC. The application of alkali-modification HC in As-contaminated soil not only enhances soil properties but also augments the potential population of dominant microorganisms that promote soil arsenic mobilization, thereby improving arsenic mobilization capacity in mining soil. This study offers a viable strategy for enhancing the phytoremediation efficiency of As-contaminated soil and establishing a recycling system for As hyperaccumulator resources in the future. [ABSTRACT FROM AUTHOR]

The decarbonization of transportation plays a crucial role in mitigating climate change, and biodiesel has emerged as a promising solution due to its renewable and eco-friendly nature. However, in order to maintain the momentum of the "green trend" and ensure energy security, an ecologically friendly pathway is important to produce efficient biodiesel. In this work, activated carbon (AC) obtained from rice husk (RH) is hydrothermally prepared and modified through cobalt transition metal for catalyst support for the transesterification process. The physicochemical characteristics of the synthesized catalysts are examined using XRD, FTIR, SEM and EDS, TGA, and BET, while the produced biodiesel is also characterized using Gas Chromatography and Mass Spectroscopy (GC-MS). To optimize the transesterification process, Fatty Acid Methyl Esters (FAME) are produced by the conversion of waste cooking oil. Response Surface Methodology (RSM) is used to validate temperature (75 °C), the methanol-to-oil molar ratio (1:9), catalyst weight percentage (2 wt.%), and retention time (52.5 min). The highest conversion rate of waste cooking oil (WCO) to biodiesel was recorded at 96.3% and tested as per American Society for Testing and Materials (ASTM) standards. Based on the results, it is clear that cobalt-loaded rice husk-based green catalyst (RHAC-Co) enhanced catalytic activity and yield for biodiesel production. Further research should focus on engine performance evaluation and scaling up of the catalyst by optimizing it for the industrial scale. [ABSTRACT FROM AUTHOR]

In this study, the optimum hydrothermal conditions of sugar beet pulp were investigated by Response Surface Methodology (RSM) based on Central Composite Design (CCD). The hydrochar obtained from sugar beet pulp (SBP) was optimized for maximum yield and carbon content. Process conditions were chosen with reaction temperatures of 200–240 °C, residence time 60–150 min, and biomass to water ratio of 1:3–1:10. The yield and carbon content of the hydrochar varied with the process parameters. In order to obtain hydrochar with the highest yield and carbon content in optimization, the reaction temperature should be 220.74 °C, the biomass to water ratio should be 1:3, and the residence time should be 95.58 min. High heating value, energy and mass yield, and energy densification ratio of sugar beet pulp and hydrochar were also investigated. The products were characterized using FT-IR, SEM, and ultimate analysis techniques. The Coats-Redfern method was used to estimate the kinetic parameters of the combustion processes. The activation energy values of SBP and SBP-HC products were calculated as 13.88 and 11.46 kJ/mol, respectively. The kinetic data were used to determine the thermodynamic parameters (ΔH, ΔG, and ΔS). As a result, the properties of hydrochar produced from sugar beet pulp under optimum conditions have been extensively investigated and the results have shown that hydrochar has potential for use in different areas. [ABSTRACT FROM AUTHOR]

Agriculture and food processing waste valorization is a sustainable process to protect the environment and to produce high added–value products. In this context, this study focuses on the conversion of two abundant agrifood residues largely available in Algeria, namely date pits and olive stones into carbonaceous materials. These biomasses were hydrothermally carbonized at 220 °C for various residence times ranging between 10 and 48 h. Then, the derived hydrochars were activated at 750 °C for 1 and 3 h under a carbon dioxide (CO2) atmosphere. Several techniques were used to characterize the obtained carbonaceous materials including gas adsorption, scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Raman, and X-ray diffraction spectroscopy. Results showed that the obtained hydrochars present high mass yields, important amounts of oxygen groups, relatively low porosities, and low specific surface area (less than 24 m2/g for all hydrochars). However, the derived activated carbons (after 1 h of CO2 activation) show an increase of specific surface areas to 449 and 562 m2/g for date pits and olive stones, respectively. Moreover, the hydrochar activation process leads also to the development of both narrow and large micropores. The increase in the residence time favors the formation of carbon microspheres and increases the microcrystallites (aromatic rings). This spherical structure development is significantly promoted after the activation process. Therefore, the produced activated carbons have interesting textural, structural, and chemical properties indicating their potential for pollutants removal from aqueous and gaseous effluents. [ABSTRACT FROM AUTHOR]

A novel silver-doped hydrochar (Ag-HC-230) was synthesized at 230 °C via hydrothermal carbonization of Tectona grandis seeds (TGs). The characteristic properties of the Ag-HC-230 were investigated using FTIR, XRD, TGA, SEM and surface area measurements. These results were further utilized for exploring the removal efficiency of the prepared material for chemical and biological contaminants. The surface area and pore volume of Ag-HC-230 were observed to be 24.9 m2g−1 and 0.073 cm3g−1, respectively. The ultimate analysis demonstrated that the prepared adsorbent was rich in C content (67.77%) as compared to N, H and S content. An ingenious investigation on the antibacterial and adsorptive performance of Ag-HC-230 was evaluated too. The antibacterial performance of Ag-HC-230 was analysed by the agar well diffusion method against the cultured suspensions of S. aureus and E. coli. To provide a better insight of Ag-HC-230, the removal of acridine yellow G (AYG) was also studied and the experimental removal capacity was found to be 0.073 mmolg−1 which was higher than undoped hydrochar HC-230-4 (0.058 mmolg−1). The kinetic experimental data were tested by fitting with different kinetics models, and the PSO model was found to be effectively applicable. The adsorption data of AYG on Ag-HC-230 were evaluated using Temkin, Freundlich, Langmuir and D-R among which the data well fitted with the Langmuir model. [ABSTRACT FROM AUTHOR]

A self‐healable hydrogel for advanced authentication applications was successfully developed. In the presence of an aqueous solution of ammonium hydroxide as a cheap passivating agent, the hydrothermal carbonization of cellulose diacetate extracted from rice straw yielded nitrogen‐doped carbon dots (NdCD) in a straightforward and ecologically beneficial manner. NdCD achieved a maximum quantum yield of 25.11%. Self‐healing biocomposite inks with different emission properties were created by using different concentrations of NdCD nanoparticles (NPs). In order to create a transparent layer of NdCD@PLA hydrogel, stamps were used to press homogenous films onto paper surfaces. Polylactic acid (PLA) hydrogel was embedded with NPs of NdCD. Self‐healing security hydrogel inks are highly durable. The NdCD@PLA hydrogel is efficiently self‐healable at room temperature. The current NdCD@PLA hydrogel can attach to different surfaces, such as glasses, plastics, and papers. The self‐healable nanobiocomposite was photostable when exposed to UV light. Under UV light, NdCD‐containing nanobiocomposite inks have a bluish color, as proved by both colorimetric parameters and fluorescence spectra. The morphological properties of NdCD were studied by transmission electron microscopy to suggest a particle diameter of 10–15 nm. The morphology of the fluorescent prints was analyzed using a number of different analytical methods. The hydrogel rheology and the mechanical performance of printed papers were tested. The printed films showed excitation and fluorescence bands at 401 and 488 nm, respectively. The present smart ink shows significant promise as a potential industrial production technique to simply produce anti‐counterfeiting prints. Highlights: Rice straws were used to prepare nitrogen‐doped carbon dots with a quantum yield of 25.11%.Self‐healable polylactic acid hydrogel was immobilized with N‐doped carbon dots (10–15 nm).Transparent printed films shifted in color to blue (488 nm) when excited at 401 nm.Ultraviolet‐stimulated photochromic authentication prints were prepared.Printed paper demonstrated non‐cytotoxicity, high photostability, and durability. [ABSTRACT FROM AUTHOR]

In the face of the rapid rise in global waste production and the pressing need to shift towards sustainable energy options, advanced Waste-to-Energy (WtE) technologies have emerged as a highly promising solution. These innovative technologies effectively utilize waste as a valuable resource, presenting a viable pathway for sustainable energy recovery and making a substantial contribution to the principles of the circular economy paradigm. This review provides a comprehensive overview of advanced WtE technologies, including thermal, biological, and chemical methods, such as gasification, pyrolysis, plasma arc gasification, anaerobic digestion, fermentation, transesterification, and hydrothermal carbonization. The efficiency of these technologies is evaluated based on their energy recovery potential, environmental impact, and economic feasibility. Case studies on successful implementations of advanced WtE technologies are analyzed to highlight their practicality and effectiveness. Finally, the paper addresses technical, regulatory, and policy challenges in this field and provides future perspectives. The objective is to underscore the role of advanced WtE technologies in achieving a sustainable and resource-efficient circular economy. [ABSTRACT FROM AUTHOR]

Cooked rice and the vegetables like lettuce are common kitchen waste, which are carbonaceous materials and have the potential as feedstock for the production of activated carbon. Cooking is similar to hydrothermal treatment (HTC), which might impact the subsequent activation of kitchen waste. In this study, the HTC of lettuce, rice, or their mixture and the activation of the resulting hydrochars were conducted. The results indicated that cross-polymerization between the N-containing organics from lettuce and the sugar derivatives from rice took place in their co-HTC, which significantly increased the hydrochar yield. Activation of the hydrochar from the co-HTC generated the AC with a yield of 2 times that from direct activation of mixed lettuce/rice. However, the co- HTC facilitated aromatization, reducing reactivity with K2C2O4 in activation and producing the AC with main micropores and low specific surface area. Activation of the hydrochar from HTC of rice followed the above trend, while that from lettuce was the opposite. The organics in lettuce were thermally unstable and could not undergo sufficient aromatization. The activation of hydrochar from HTC of lettuce thus generated the AC with the lowest yield, but the highest specific surface area (1684.9 m²/g), abundant mesopores, and superior capability for adsorption of tetracycline. However, the environmental impacts and energy consumption for the production of AC from the hydrochar of lettuce were higher than that from hydrochar of co-HTC. [ABSTRACT FROM AUTHOR]

Small biomass piece, huge power—a fulcrum to lift two global lifelines, where water and energy meet. Initiative of new-to-nature electron–ion nexus and inter-functional synergy showcased sustainable integration between over-limit solar-evaporative desalination, even in backlit environments, and robust long-term all-day clean electricity co-generation. Sparks were created when intersecting with engineering. [Display omitted] The water–energy nexus has garnered worldwide interest. Current dual-functional research aimed at co-producing freshwater and electricity faces significant challenges, including sub-optimal capacities ("1 + 1 < 2"), poor inter-functional coordination, high carbon footprints, and large costs. Mainstream water-to-electricity conversions are often compromised owing to functionality separation and erratic gradients. Herein, we present a sustainable strategy based on renewable biomass that addresses these issues by jointly achieving competitive solar-evaporative desalination and robust clean electricity generation. Using hydrothermally activated basswood, our solar desalination exceeded the 100% efficiency bottleneck even under reduced solar illumination. Through simple size-tuning, we achieved a high evaporation rate of 3.56 kg h−1 m−2 and an efficiency of 149.1%, representing 128%–251% of recent values without sophisticated surface engineering. By incorporating an electron–ion nexus with interfacial Faradaic electron circulation and co-ion-predominated micro-tunnel hydrodynamic flow, we leveraged free energy from evaporation to generate long-term electricity (0.38 W m−3 for over 14 d), approximately 322% of peer performance levels. This inter-functional nexus strengthened dual functionalities and validated general engineering practices. Our presented strategy holds significant promise for global human–society–environment sustainability. [ABSTRACT FROM AUTHOR]

Carbon-based nanodots have garnered recent interest for their simple synthesis and versatile utility, ranging from biomedical to (opto) electronic applications, evolving into a tunable and biocompatible material. Here, for the first time, a biochar (lotus leaf) derived carbon nanodots was synthesized through hydrothermal carbonization. The synthesized hollow spherical biochar was engineered via functionalization by grafting –SO3H active sites. The attained catalyst was broadly analyzed by XRD, FTIR, TGA, BET, SEM–EDX, TEM, and XPS analysis after which it was applied for the acetalization reaction of crude glycerol (a biodiesel by-product) to form solketal, a potential fuel additive to valorize the large waste stream generated from biodiesel industry. Employing the RSM-CCD methodology, the experimental matrix was executed, and subsequent data were scrutinized through multiple regressions to model a quadratic equation. Under specific reaction parameters—a reaction duration of 14 min, a molar ratio of 7.5:1, and a catalyst loading of 5.7 wt.%, maximum solketal yield (95.7%) was attained through the ultrasonication method. Finally, to conclude, life cycle cost analysis (LCCA) for solketal production was studied here which determined the overall cost of solketal production per kilogram to be 0.719 USD ($), indicating high commercial applicability. [ABSTRACT FROM AUTHOR]

Metal-free nanocarbons with highly editable compositions and well-defined morphologies, and adjustable coordination environments have been considered as promising and inexpensive electrode materials that can be used in the fields of fuel cells and metal-air batteries. Herein, the typical micromorphology of high-output tuber crops potato was examined for the first time by cryo-electron microscopy, and nitrogen-doped spherical carbons with highly curved carbon layers were prepared from potato and sweet potato by hydrothermal and ammonia-activated treatments. The potato-derived carbon (PC) and sweet potato-derived carbon (SPC) with enriched nitrogen dopants on native curved carbon layers exhibit favorable oxygen reduction reaction (ORR) activities in both acidic and alkaline media. The half-wave potential of the curved PC is 60 mV higher than that of commercial Pt/C (20 wt% Pt) in 0.1 M KOH. Impressively, the zinc-air battery using the curved PC displays excellent stability and achieves a peak power density of 116 mW cm−2, surpassing the performance of Pt/C (108 mW m−2). Finite element method (FEM) simulations and molecular dynamics (MD) calculations reveal that the curved carbon surface-enhanced tip electric field on the spherical structure, could further induce charge transfer and accelerate the ORR process. This work elucidates the origin of the catalytic activity of spherically structured metal-free carbons with N-doping, providing meaningful insights into the development of low-cost and highly active catalysts and advancing the field of sustainable energy. [Display omitted] • The morphology of potato abundant spherical starch granules was characterized. • Spherical carbons with doped N were constructed by hydrothermal carbonization. • Zinc-air batteries assembled with catalysts have higher power density than Pt/C. • FEM indicates the curved carbon layer enhanced tip electric field accelerate ORR. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) is considered as a potential material for electrodes in supercapacitors; however, its production process entails significant emissions to the environment. This study aims to assess the environmental impacts of manufacturing AC and electrodes for supercapacitors from waste materials, utilizing the life cycle assessment (LCA) principles. The process of producing AC involves raw material preparation, hydrothermal carbonization, and chemical activation processes, utilizing potassium hydroxide (KOH) as a chemical agent. The environmental impact of AC production and fabrication of AC electrodes was analyzed using the SimaPro software. A cradle-to-gate study was conducted to analyze the production of 1 kg of AC and one electrode from waste materials, including oil palm leaves, Sesbania, and filter cake, chosen based on the local availability in the study area. Life cycle data were compiled from the laboratory, ecoinvent database, and calculations based on the mass and energy balance. Using the ReCiPe midpoint (H) characterization method, potential environmental impacts were computed across eighteen categories. Sesbania AC exhibited the highest impact across fourteen out of eighteen categories for producing 1 kg of AC, with the largest impact observed in the marine ecotoxicity category due to the presence of KOH in the chemical activation process. For producing 1 farad (F) electrode, Sesbania showed the lowest environmental impact due to its high specific capacitance. Its environmental impacts of producing a 1 F electrode were unexpectedly lower than those of oil palm leaves because the predominant environmental impacts were from hydrothermal carbonization and pretreatment rather than KOH activation. Additionally, Sesbania exhibited significantly higher yields in hydrothermal carbonization, resulting in the use of relatively fewer materials and less energy, thereby leading to reduced impacts compared to other materials. The developed AC electrode showed excellent performance in several environmental impact categories, with AC production being the main contributor. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) stands out as an eco-friendly, cost-effective method for generating renewable carbon-based materials from biomass. The HTC process yields products such as hydrochars and carbon dots (CDs), possessed of notable photocatalytic capabilities due to their unique physicochemical features. Additionally, pairing traditional photocatalysts with hydrochar derivatives elevates their performance, rendering them more effective. Recent times have witnessed a surge in interest in these hydrochar based photocatalysts (HC-photocatalysts). Their appeal stems from multiple attributes: impeccable performance, adaptability to visible light, and adjustable physicochemical properties. This review delves deep into the evolving landscape of these HC-photocatalysts, segmenting them into three distinct categories: hydrochars, hydrochar-based CDs (HC-CDs), and hydrochar-based composites (HC-composites). For each category, we dissect their synthesis routes, unravel the photocatalytic mechanisms, and explore various enhancement strategies. We further traverse their versatile applications, spanning environmental treatment, disinfection, energy conversion, and organic synthesis. In the end, we spotlight the prevailing challenges and uncharted territories in the domain of HC-photocatalysts. In essence, this review serves as a guide, furnishing a theoretical foundation and steering directions for future explorations and tangible implementations of HC-photocatalysts. Highlights: Biomass can be converted into highly efficient photocatalysts by HTC. Photocatalytic mechanisms and modifications of hydrochars and HC-CDs are discussed. The roles of carbons in HC-composite photocatalysts are reviewed. HC-photocatalysts have shown various environmental, energy and other applications. Prospects and guidelines for theoretical and application research are listed. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) management poses significant challenges due to the generation of organic waste materials, including the under-sieve fraction (USF), which contains high moisture and organic content. Hydrothermal carbonization (HTC) has emerged as a promising technology for converting USF into hydrochar (HC), a valuable energy-rich material with improved combustible properties. Despite the potential of HTC for waste valorization, comprehensive studies on the thermoecological cost (TEC) and environmental implications of applying HTC to USF are limited. In this study, a detailed analysis of the TEC associated with the HTC process applied to USF from MSW was conducted. The TEC assessment was conducted considering varying dilution ratios (DS/W), operational temperatures (180–220 °C), and reaction times (1–8 h) to evaluate the energy efficiency, resource utilization, and environmental impact of the HTC process. Comparative assessments were made with alternative USF treatment methods, such as bio-stabilization, landfilling, and wastewater treatment. The results indicate that the optimal conditions for minimizing TEC are a temperature of 180 °C, a reaction time of 1 h, and a dilution ratio of 0.15, achieving a TEC value of approximately 9.25 GJ per ton of USF. This represents a significant reduction compared to the conventional treatment methods, which showed a TEC of 14.9 GJ/ton of USF. This study provides a comprehensive comparison of HTC with alternative USF treatment methods, such as bio-stabilization and landfilling, highlighting HTC's superior energy efficiency and environmental sustainability. These findings offer valuable insights into the energy consumption, resource utilization, and environmental impact of HTC, emphasizing its potential for sustainable waste valorization. [ABSTRACT FROM AUTHOR]

To address the problem of the low nitrogen (N) content of carbon materials prepared through the direct carbonization of food waste, soybean meal and egg whites with high N contents were selected to carry out carbonization experiments on food waste. At 220 °C, the effects of hydrothermal carbonization and microwave carbonization on the properties of supercapacitor electrode materials were investigated. The results show that food waste doped with soybean meal and egg whites could achieve good N doping. At a current density of 1 A·g−1, the specific capacitance of the doped carbon prepared by hydrothermal doping is as high as 220.00 F·g−1, which is much greater than that of the raw material prepared through the hydrothermal carbonization of food waste alone, indicating that the hydrothermal carbonization reactions of soybean meal, egg white, and food waste promote the electrochemical properties of the prepared carbon materials well. However, when a variety of raw materials are mixed for pyrolysis carbonization, different raw materials cannot be fully mixed in the pyrolysis process, and under the etching action of potassium hydroxide, severe local etching and local nonetching occur, resulting in a severe increase in the pore size distribution and deterioration of the electrochemical performance of the prepared carbon materials. At a current density of 1 A·g−1, the specific capacitance of these prepared carbon materials is 157.70 F·g−1, whereas it is only 62.00 F·g−1 at a high current density of 20 A·g−1. Therefore, this study suggests that the hydrothermal carbonization process is superior to the microwave pyrolysis carbonization process for preparing supercapacitor electrode materials with multiple samples doped with each other. [ABSTRACT FROM AUTHOR]

This paper explores the intricate relations between biomass polymeric composition, thermochemical conversion routes, char yields and features in order to advance the knowledge on biomass conversion processes and customize them to meet specific requirements. An exhaustive characterization has been performed for three types of biomasses: (i) spruce bark, a woody primary and secondary residue from forestry and wood processing; (ii) wheat straws—agricultural waste harvest from arable and permanent cropland; and (iii) vine shoots, a woody biomass resulting from vineyard waste. Chemical (proximate and ultimate analysis), biochemical, trace elements, and thermal analyses were performed. Also, Fourier transform infrared spectroscopy, Scanning Electron Microscopy, and thermogravimetric analysis were conducted to establish the compositional and structural characteristics of feedstock. The main polymeric components influence the amount and quality of char. The high hemicellulose content recommends wheat straws as a good candidate especially for hydrothermal carbonization. Cellulose is a primary contributor to char formation during pyrolysis, suggesting that vine shoots may yield higher-quality char compared to that converted from wheat straws. It was shown that the char yield can be predicted and is strongly dependent on the polymeric composition. While in the case of spruce bark and wheat straws, lignin has a major contribution in the char formation, cellulose and secondary lignin are main contributors for vine shoots char. [ABSTRACT FROM AUTHOR]

In this work, highly efficient carbon‐supported Pd‐based catalysts for formic acid dehydrogenation were synthesized by a straightforward wet impregnation‐reduction method. The carbon support was obtained from a biomass residue (almond shell) prepared via H3PO4‐assisted hydrothermal carbonization (HTC) and thermal activation. This carbon support was doped with nitrogen groups to study the effect on the electronic properties and catalytic performance of the catalysts. Investigating the formation of PdAg alloys with varying Pd : Ag molar ratios resulted in catalysts exhibiting enhanced catalytic activity compared to monometallic Pd counterparts. Notably, the Pd1Ag0.5/NAS catalyst displayed outstanding catalytic performance, achieving an initial TOF of 1716 h−1 (calculated in the first 3 minutes of reaction and expressed per mole of Pd) and maintaining substantial activity over 6 consecutive reaction cycles. This work elucidates the successful synthesis of effective catalysts, emphasizing the influence of nitrogen doping and PdAg alloy composition on catalytic behavior and stability. [ABSTRACT FROM AUTHOR]

The hydrothermal carbonization (HTC) technique and subsequent pyrolysis were applied. Herein, two different types of biobased feedstocks, sucrose (Suc) and Miscanthus (Mis), were chosen. Urea served as N precursor for the in situ doping. HTC of Suc and Mis with urea leads to N‐doped hydrochars (N‐HCs). Suc and Mis decompose in different, complex degradation pathways, which leads to the emergence of N‐HCs consisting of distinct ratios of N‐containing primary chars (N‐PCs) and secondary chars (N‐SCs). After pyrolysis, maximum N contents of 5.6 wt % and 4.8 wt % of the N‐doped pyrolyzed hydrochar (N‐PHC) electrodes from Suc and Mis, respectively were reached. The role of PC and SC formation on the impact of N‐doping in the context of physicochemical properties of the N‐PHCs was compared with each other. In this study, they were tested with respect to the influence of N‐PCs and N‐SCs on their electrochemical performance in energy storage application. It turned out that the electrical conductivity (EC) and specific capacitances increased. Highest EC value of 129.1 S ⋅ cm−1 was obtained with N‐PHC based on Suc. Simultaneously, enhanced average specific capacitances of 47.0 F ⋅ g−1 at 5 mV ⋅ s−1 and 3.5 F ⋅ g−1 at 100 mV ⋅ s−1 are ascertained with N‐PHCs from Suc and Mis, respectively. [ABSTRACT FROM AUTHOR]

N-containing biochar from oatmeal was produced by co-pyrolysis of hydrochar, ZnCl2, and FeCl3, showing well-developed pores with surface areas of 2744 m2/g and N species of 5.4 at.%. The as-formed biochar was used for Cr(VI) removal via batch adsorption, and the different parameters, i.e., initial pH, contact time, and concentration on efficiency, were evaluated. Adsorptive results indicated that Cr(VI) removal is largely affected by surface areas and functional groups of biochar under optimum pH value of two, following by pseudo-second-order and Langmuir model. The maximum capacity for Cr(VI) is up to 139 mg/g from synergistic effect of adsorption and reduction mechanism, much higher than that of analogous in the absence of FeCl3 with capacity of 113 mg/g and commercial activated carbons of 61 mg/g. N-containing biochar also had superior recyclability with capacity still up to 67.5 mg/g even after ten times recycling. The inexpensive feedstock and high removal performance made the present biochar be a promising candidate for Cr(VI) removal from wastewater. [ABSTRACT FROM AUTHOR]

To reveal the influence of the diversity of precursors on the formation of environmental persistent free radicals (EPFRs), pomelo peel (PP) and its physically divided portion, pomelo cuticle (PC), and white fiber (WF) were used as precursors to prepare six hydrochars: PPH-Fe, PCH-Fe, WFH-Fe, PPH, PCH, and WFH with and without Fe(III) addition during hydrothermal carbonization (HTC). PPH-Fe and WFH-Fe had higher EPFRs content (9.11 × 1018 and 8.25 × 1018 spins·g−1) compared to PPH and WFH (3.33 × 1018 and 2.96 × 1018 spins·g−1), indicating that iron-doping favored EPFRs formation. However, PCH-Fe had lower EPFRs content (2.78 × 1018 spins·g−1) than PCH (7.95 × 1018 spins·g−1), possibly due to excessive iron leading to the consumption of the generated EPFRs. For another reason, the required Fe(III) amount for EPFRs formation might vary among different precursors. PC has a lower concentration of phenolic compounds but 68–97% fatty acids, while WF and PP are rich in cellulose and lignin. In the Fenton-like reaction, oxygen-centered radicals of hydrochar played a significant role in activating H2O2 and efficiently degrading bisphenol A (BPA). Mechanisms of reactive oxygen species (ROS) generation in hydrochar/H2O2 system were proposed. EPFRs on hydrochar activate H2O2 via electron transfer, creating ·OH and 1O2, leading to BPA degradation. More importantly, the embedded EPFRs on the hydrochar's inner surface contributed to the prolonged Fenton-like reactivity of PPH-Fe stored for 45 days. This study demonstrates that by optimizing precursor selection and iron doping, hydrochars can be engineered to maximize their EPFRs content and reactivity, providing a cost-effective solution for the degradation of hazardous pollutants. Article Highlights: Characteristics and mechanisms for the generation and consumption of EPFRs were proposed. To favor g3-type EPFRs formation, the quantity of Fe(III) and aromatic compounds of the biomass should be matched. The g3-type EPFRs on hydrochars played a major role in the Fenton-like reaction. The external EPFRs of hydrochars were consumed easily while the internal EPFRs persisted during long-term storage. [ABSTRACT FROM AUTHOR]

Food waste production reaches actually about 1.3 billion tonnes per year, corresponding to the emission of 3.3 billion tonnes equivalent of CO2, thus calling for improved recycling. Here we review food waste conversion into energy and products such as biohydrogen, biogas, biofuel, biodiesel, biochar, bioplastics, fertilizers, animal feed, organic acids, enzymes, and proteins. Food waste can be treated by incineration, pyrolysis, composting, anaerobic digestion, hydrothermal carbonization, and landfilling. Properties of food waste influence the efficiency of conversion. [ABSTRACT FROM AUTHOR]

Carbon capture and conversion technology is the main method to reduce carbon dioxide emissions. Porous carbon with large surface area, excellent thermal stability and low-cost has a wide application potential in the field. In this study, nitrogen-doped porous carbon is prepared by hydrothermal carbonization and chemical activation with methyl cellulose and melamine as carbon precursor and nitrogen sources. The effects of activating agent and nitrogen-doping ratios on the structure and electrocatalytic reduction performance are studied. The sample prepared under optimized conditions has a specific surface area of 1417 m2 g−1, total pore volume of 0.9 cm3 g−1, micropore volume of 0.36 cm3 g−1, as well as abundant nitrogen active sites. It exhibits a high CO Faraday efficiency (91%) at overpotential of -0.61 V (vs. RHE), together with a good cycling of long-term stability. [ABSTRACT FROM AUTHOR]

This review explores the utilization of lignocellulosic biomass (LCB) waste in the fabrication of graphene and its applications in hydrogen storage. Several LCB wastes, such as rice straws, coconut shells, wheat straws, and sugarcane bagasse, along with the methodology used and the characteristics of the final graphene, have been discussed in detail. It was found that the coconut shells produced crumpled multilayered graphene, rice husks (RHs) provided a mix of graphene layers and amorphous carbon, wheat straw yielded few‐layered graphene, and sugarcane bagasse contributed to different graphene‐like materials. This review has also focused on the various synthesis processes, such as carbonization, hydrothermal carbonization (HTC), chemical activation, pyrolysis, chemical vapor deposition (CVD), and Hummers' method for graphene fabrication from LCB waste, along with their advantages and disadvantages, for a better understanding. Various results have been discussed exploring the use of lignocellulosic biomass‐derived graphene (LCB‐G) and its various modified forms for hydrogen storage applications. Various challenges in graphene fabrication from LCB, such as low yield, product quality, scalability, use of expensive synthesis methods, and toxic chemicals, along with some potential solutions, have been mentioned. Finally, the review concludes with insights into the future of LCB‐G and its role in hydrogen storage while identifying some gaps, such as scalability and product quality, for further research and development. [ABSTRACT FROM AUTHOR]

The urgent need for sustainable waste management strategies has led to the exploration of innovative approaches for the valorization of waste. In this study, a method is proposed for carbonizing waste biomass materials, particularly paper mill waste sludges (primary and biological) and knots, to produce porous carbonaceous supports. Through an initial hydrothermal carbonization followed by carbonization with nitrogen flow, porous carbon materials are successfully generated. The findings of this investigation validate the successful generation of effective carbonaceous supports utilizing waste biomass materials. These materials are then evaluated for their effectiveness as porous supports in the ionic liquid‐catalyzed cycloaddition reaction of CO2 to styrene oxide, achieving a remarkable conversion rate of up to 98% and an impressive selectivity exceeding 99%. Additionally, the results underscore the significant impact of the selected IL on the overall conversion process. Overall, this study presents a promising pathway for the valorization of paper mill waste sludge through the production of porous carbon materials with potential applications in catalysis and beyond. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising method for the conversion of agricultural and agro-industrial residues into valuable products. HTC processes biomass through chemical reactions that produce hydrochar, a carbon-rich solid similar to lignite. Unlike other thermochemical processes, HTC can handle high-moisture biomass without pre-drying. This article evaluates the efficiency of HTC on wood chips, wheat straw, and grape pomace, examining their chemical and structural characteristics and critical operational parameters such as the temperature, pressure, biomass/water ratio, and reaction time. The obtained results highlight that the two key process parameters are the temperature and the ratio between the solid biomass and liquid phase. Increasing the first parameter increases the energy content by 20% and increases the carbon concentration by up to 50%, while reducing the oxygen content by 30% in the hydrochar. Varying the second parameter leads to the alternating reduction of the ash content but simultaneously reduces the energy content. The reaction time seems to have a limited influence on the quality parameters of the biochar produced. Lastly, HTC appears to successfully enhance the overall quality of widely available agricultural wastes, such as grape pomace. [ABSTRACT FROM AUTHOR]

Livestock manure and crop residues are significant sources of phosphorus. However, the ineffectiveness of current processing technologies often leads to the suboptimal recovery of this phosphorus, causing considerable resource wastage and environmental pollution. Recently, global research has increasingly been focused on the resource recovery of organic waste materials using hydrothermal carbonization technology. This study investigated variations in phosphorus forms in the hydrochar produced from swine manure and rice straw, employing diverse hydrothermal carbonization conditions and applying the Box–Behnken response surface methodology and Hedley's phosphorus fractionation method. The results indicated that inorganic phosphorus predominates in the hydrochar, with organic phosphorus comprising 5–30% of the total phosphorus. Furthermore, the study found that the available phosphorus content, as measured by NaHCO3 extraction, decreased as the reaction time and temperature of the hydrothermal carbonization process increased. The concentrations of H2O-P and NaHCO3-P fractions decreased with increasing reaction times and temperatures but increased with a higher swine manure-to-straw ratio. Conversely, the concentrations of NaOH-P and HCl-P fractions showed an increasing trend with rising reaction temperature, prolonging reaction time, andusing a high swine manure-to-straw ratio. Consequently, this study offers vital theoretical and practical insights into the resource utilization of livestock manure and crop straw, significantly contributing to the challenges of waste management and environmental sustainability in agriculture. [ABSTRACT FROM AUTHOR]

Three-dimensional hierarchical porous carbons (HPCs) created through hydrothermal carbonization and the subsequent chemical activation of miscanthus were tested as adsorbents of Pb2+ and methylene blue from the aqueous solution. The HPC pore structure was customized using various hydrochar precursors obtained through a longer reaction time and by adding acetic acid. HPC obtained from hydrochar derived from acetic acid's addition exhibited the highest specific surface area due to a larger micropore volume. This adsorbent proved to be the most efficient in removing lead from aqueous solutions. The Langmuir isotherm best described the lead adsorption process onto HPC with qm = 155.6 mg g−1 and the pseudo-second-order kinetic model. HPC obtained from hydrochar produced with a longer reaction time exhibited improved methylene blue adsorption properties. The pseudo-second-order kinetic model and the Freundlich isotherm best described the experimental data. The theoretical maximum adsorption capacity for methylene blue was 316.0 mg g−1. The type of hydrochar significantly impacted the yield and physical structure of HPCs, while having a lesser effect on the composition of surface functional groups. The results revealed the binding mechanism of each pollutant, highlighting the importance of biomass pretreatment on the structure of the resulting HPC and its effectiveness in water purification. [ABSTRACT FROM AUTHOR]

Abstract\nNOVELTY STATEMENTThis work reports new findings on the preparation of hydrochar from date palm (Phoenix dactylifera) seeds through the application of the microwave hydrothermal carbonization (HTC) method. Optimization investigations involving temperatures and reaction times were conducted to establish the highest yield, achieving a maximum yield of 60.87%. The prepared material was then impregnated in phosphoric acid and carbonized in the tube furnace at 550 °C for 1.5 h with a nitrogen flow of 50 CCM. The samples were characterized via scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET) and Fourier transform infrared (FTIR). The samples showed remarkable BET surface areas following activation, reaching up to 992 m2·g−1. The substance was subsequently used to absorb methylene blue with good fitting to the Freundlich and Redlich-Peterson isotherm and achieved a peak adsorption capacity of 196.6 ± 3.9 mg·g−1.This study involves the preparation of hydrochar through microwave-assisted hydrothermal carbonization (HTC) of date palm seeds. It explores the impact of different process parameters, such as power, reaction temperatures, and timing on the mass yield and BET surface area of the hydrochars. Additionally, the prepared material undergoes chemical activation with phosphoric acid, and its efficacy in extracting methylene blue (MB) from an aqueous solution is assessed. This research is particularly novel as it represents the first comprehensive investigation into the use of microwave-derived and phosphoric acid-activated hydrochar for MB extraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influence of pre-drying methods on HTC of sewage sludge was evaluated. • Pre-drying affected the composition and pyrolysis/combustion behavior of sludge. • Pre-drying limitedly affected hydrochar yield, composition, and characteristics. • The quality of sludge hydrochar with and without pre-drying is comparable. While pre-drying of sewage sludge prior to hydrothermal carbonization is rarely practiced, various pre-drying methods have been performed in literature at lab-scale for convenient solid-to-liquid ratio adjustment. This has created a barrier for comparing hydrochar quality between different studies. Given pre-drying can destroy the floc structure of sewage sludge, we hypothesize that pre-drying may promote the hydrolysis step during hydrothermal carbonization process, resulting in improved hydrochar quality with low nitrogen content. In the current study, the influence of different pre-drying methods (freeze-dry, air-dry and vacuum-dry at 70 °C and 105 °C) on the subsequent hydrothermal carbonization of sewage sludge at 220 °C was assessed in terms of sewage sludge and hydrochar's chemical composition, fuel properties, pyrolysis and combustion behavior, as well as the characterization of the liquid phase. The results indicate that although pre-drying impacts sewage sludge's chemical composition, pyrolysis and combustion behavior, no significant differences exist in the yield, chemical composition, fuel properties, and pyrolysis and combustion behavior of the hydrochar. Therefore, the use of pre-drying would not affect the hydrothermal carbonization process of sewage sludge, and a comparison can be made on hydrochar quality between different studies with or without pre-drying. [ABSTRACT FROM AUTHOR]

The optimal process conditions concerning the hydrothermal carbonization of digested sewage sludge are crucial to the economically effective technology needed to produce a solid product, hydrochar, for energy purposes. Accordingly, different residence times, 0.5 h, 1 h and 2 h, were investigated in order to understand the effect of residence time on the process. Furthermore, the physical and chemical properties of hydrochar were investigated and compared to the raw material. For these reasons, analyses describing fuel properties were performed, including ultimate and proximate analyses, HHV, and TGA analysis. The latter method was employed to study the combustion process of solid samples. In addition, the oxide content of different elements within the ash of solid samples was determined using the XRF method to calculate indices related to operational problems during the combustion process. The results confirmed that time did not matter significantly and the physical and chemical properties of hydrochar were very similar to each other. However, the contact angle for 2 h of residence time confirmed that a longer processing time resulted in a more hydrophobic character of hydrochar and enabled more effective dewaterability of hydrothermal slurry. It was also noted that the hydrothermal carbonization process affected the sewage sludge in a positive way. In brief, the results confirmed that the hydrochar was a brittle, moderately hydrophilic, solid carbon-containing product that provided a different combustion performance than the raw sewage sludge. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) serves as a sustainable method to transform pine needle waste into nitrogen-doped (N-doped) hydrochars. The primary focus is on evaluating these hydrochars as catalytic electrodes for the oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR), which are pivotal processes with significant environmental implications. Hydrochars were synthesized by varying the parameters such as nitrogen loading, temperature, and residence time. These materials were then thoroughly characterized using diverse analytical techniques, including elemental analysis, density measurements, BET surface area analysis, and spectroscopies like Raman, FTIR, and XPS, along with optical and scanning electron microscopies. The subsequent electrochemical assessment involved preparing electrocatalytic inks by combining hydrochars with an anion exchange ionomer (AEI) to leverage their synergistic effects. To the best of our knowledge, there are no previous reports on catalytic electrodes that simultaneously incorporate both a hydrochar and AEI. Evaluation metrics such as current densities, onset and half-wave potentials, and Koutecky–Levich and Tafel plots provided insights into their electrocatalytic performances. Notably, hydrochars synthesized at 230 °C exhibited an onset potential of 0.92 V vs. RHE, marking the highest reported value for a hydrochar. They also facilitated the exchange of four electrons at 0.26 V vs. RHE in the ORR. Additionally, the CO2RR yielded valuable C2 products like acetaldehyde and acetate. These findings highlight the remarkable electrocatalytic activity of the optimized hydrochars, which could be attributed, at least in part, to their optimal porosity. [ABSTRACT FROM AUTHOR]

The development of industrial process in line with the circular economy and the environmental, social and corporate governance (ESG) is the foundation for sustainable economic development. Alternatives that make feasible the transformation of residues in added value products are promising and contribute to the repositioning of the industry towards sustainability, due to financial leverage obtained from lesser operational costs when compared with conventional processes, therefore increasing the company competitivity. In this study, it is presented a promising and innovative technology for the recycling of agro-industrial residues, the sugarcane bagasse and the high-pressure water boiler effluent, in the development of a low-cost adsorbent (HC-T) using the hydrothermal carbonization processes and its application in the adsorption of herbicide Diuron and Methylene Blue dye from synthetic contaminated water. The hydrothermal carbonization was performed in a Teflon contained inside a sealed stainless-steel reactor self-pressurized at 200°C, biomass-to-effluent (m/v) ratio of 1:3 and 24 h. The synthesized material (HC) was activated in an oven at 450°C for 10 min, thus being named adsorbent (HC-T) and characterized by textural, structural and spectroscopic analyses. The low-cost adsorbent HC-T presented an 11-time-fold increase in surface area and ∼40% increase in total pore volume in comparison with the HC material. The kinetic and isotherm adsorption experiment results highlighted that the HC-T was effective as a low-cost adsorbent for the removal of herbicide Diuron and Methylene Blue dye from synthetic contaminated waters, with an adsorption capacity of 35.07 (63.25% removal) and 307.09 mg g−1 (36,47% removal), respectively. [ABSTRACT FROM AUTHOR]

The use of beach-cast macroalgae as a fertilizer (F) or soil amendment (SA) is coming back into focus, due to its highly efficient transformation of CO2, nutrients, salts and minerals from its aqueous surroundings into biomass. This research studied the hydrothermal carbonization (HTC) of Fucus vesiculosus macroalgae to hydrochar and evaluated its feasibility for use in soil applications. F. vesiculosus was submitted to HTC following a full factorial design of experiments with three HTC process parameters varied to assess their impact on the hydrochars: temperature (T: 160, 190, 220 °C), solid content (%So: 20, 35%), and process water recirculation (PWrec: yes and no). In general, F. vesiculosus and its hydrochars were rich in nutrients, but also contained regulated heavy metals. Investigation of the partitioning behavior of inorganic elements between the hydrochars and process water showed that heavy metals like Cr, Pb, Co and Cu tended to accumulate in the hydrochar, unaffected by HTC conditions. Nutrients such as P, N, B, and Mn were primarily found in the hydrochar and could be partially influenced to transfer to process water by changing %So and T. The correlation between the mass fractions of 22 elements in the hydrochar and HTC process parameters was studied. T was the most influential parameter, showing a significant positive correlation for eleven elements. %So and PWrec showed inconsistent effects on different elements. When process water was recirculated, some elements decreased (Ca, Cd, Fe) while others increased (K, Na, B, N) in the hydrochar. Assessment against various regulations and standards for F and SA revealed that F. vesiculosus complied with Cd limit values for most rules including the EURF and B, and was regulated only in the RAL for SA, over the limit value. In contrast, the limit value of Cd for both F and SA applications was surpassed in the 13 hydrochars. The contents of N, P, K, S, and Na in the feedstock and hydrochars complied with European F and SA rules, while they were too high for German rules on SA. The other limits for F rules were achieved (under certain HTC process parameters) except for P (lower than the requirements in F for F. vesiculosus and its hydrochars). Highlights: The brown algae complied with most limit values for Cd content to be applied as soil amendment or as fertilizer. Hydrochars from brown algae did not comply with any Cd limit values. No HTC process condition reduced the Cd content to comply with the requirements. Inorganic mass fractions were mostly influenced by temperature (positively correlated with 11/22 elements), followed by water recirculation (7) and solid content (6). Heavy metals accumulate in hydrochars across all HTC conditions. The partitioning for some elements (e.g., Cd, Co, Cu, W, V) showed no correlation with process conditions. [ABSTRACT FROM AUTHOR]

In this study, we developed a heterojunction photocatalyst, namely nitrogen-doped carbon quantum dots/titanium dioxide (N-CQDs/TiO2), for the effective and sustainable treatment of ciprofloxacin (CIP) antibiotic in aqueous solution. First, N-CQDs were prepared from a chitosan biopolymer with a green, facile, and effective hydrothermal carbonization technique and then anchored on the TiO2 surface via a hydrothermal process. The morphological, structural, and optical properties of the as-prepared materials were characterized by using advanced analytical techniques. The impacts of the mass percentage of N-CQDs, catalyst and CIP concentration, and pH on photocatalytic CIP degradation were investigated in depth. Comparative analyses were performed to evaluate different processes including adsorption, photolysis, and photocatalysis for the removal of CIP with TiO2 and N-CQDs/TiO2. The results revealed that N-CQDs/TiO2 exhibited the highest CIP removal efficiency of up to 83.91% within 120 min using UVA irradiation under optimized conditions (10 mg/L CIP, 0.4 g/L catalyst, and pH 5). Moreover, the carbon source used in the fabrication of N-CQDs was also considered, and lower removal efficiency was obtained when glucose was used as a carbon source instead of chitosan. This excellent improvement in CIP degradation was attributed to the ideal separation and migration of photogenerated carriers, strong redox capability, and high generation of reactive oxygen species provided by the successful construction of the N-CQDs/TiO2 S-scheme heterojunction. Scavenger experiments indicated that h+ and •OH reactive oxygen species were the predominant factors for CIP elimination in water. Overall, this study presents a green synthesis approach for N-CQDs/TiO2 heterojunction photocatalysts using natural materials, demonstrating potential as a cost-effective and efficient method for pharmaceutical degradation in water treatment applications. [ABSTRACT FROM AUTHOR]

In this article, carbon dots (CDs) are fabricated via hydrothermal carbonization (HTC) at different temperatures ranging from 120 to 210 °C. Regarding the temperature variations, they demonstrate a crucial role in specific identification in the ability to differentiate the chemical structures and optical properties of the resulting CD features. Both heteroatoms‐doped core structure, and the functionalized surface state display a changed that correlates with the temperature variations mentioned. The CDs which are synthesized at 180 °C contain the appropriate balance of doped heteroatoms and surface functional groups which further display the most promising performance of the quenching effect of up to 17% toward ferric ions. This work contributes to the growing understanding of CDs and provides valuable insights for the future development of applications that may favor certain interest in the creation or designing process in various applications. [ABSTRACT FROM AUTHOR]

World fishery production and its processing generate huge volumes of fish waste which cause significant challenge to public health and urban planning. The objective of this study is to prepare nanocarbon dots using tuna skin waste and to assess their effectiveness as an additive in three epoxy polymer coatings. These coatings will be applied to BIS 2062 boat building steel to study corrosion in marine environments. Fish skin-derived nanocarbon dots (FSCD) were synthesized through hydrothermal carbonization. Spectroscopic evaluation confirmed the presence of multiple fluorophores in FSCD, which suggest that molecule's structure includes a cyclic conjugated carbon core with dangling functional groups such as COOH, C=O, −OH and C–NH at the edges, resulting in blue–green fluorescence. Electrochemical characteristics of FSCD-reinforced commercial epoxy polymer (3 types)-coated BIS 2062 steel demonstrated excellent corrosion resistance in marine environment. The optimum concentrations of FSCD were determined to be 0.05% in bisphenol A and Dobeckot epoxy polymers, and 0.02% in Araldite epoxy polymer, as evidenced by the highest polarization resistance, lowest corrosion current density and capacitance. The nano-FSCD exerted a synergistic influence on pore-free polymerization due to the presence of dangling functional groups such as amines, in addition to the amine-based hardener. Therefore, fish waste-derived carbon dots offer great potential as a cost-effective and eco-friendly anticorrosive additive for epoxy polymers, meeting the majority of requirements in the anticorrosive coating industry. [ABSTRACT FROM AUTHOR]

Agricultural wastes have an important potential as an alternative to fossil fuels among renewable energy sources. In this study, solid fuel production from hazelnut husk was investigated by the hydrothermal carbonization method. Moreover, the use of hazelnut husks as an alternative biomass for solid fuel production was evaluated by considering solid fuel properties obtained from wood waste. Although there are studies on the energy value of hazelnut shells and their recovery to the economy, there are limited studies on hazelnut husks. A full-scale reactor was designed and constructed for the hydrothermal carbonization. The hydrothermal carbonization process was performed with a batch system in the reactor with an inner volume of 8 m3. The flue gas formed during the carbonization process was transferred to the reactor. The ultimate analysis and calorific values of pellets and charcoals were examined. The results show that all wastes were not well pelletized. The briquets achieved acceptable values for their thermal uses. Hazelnut husk was transformed into a valuable product with a calorific value of 4792 kcal/kg. Although wood waste had better combustion properties, the product from hazelnut husks, which is an economically worthless product, had become a valuable product due to its easy burning and high calorific value. [ABSTRACT FROM AUTHOR]

The fuel characteristics and combustion behavior of the hydrochar obtained from the co-hydrothermal carbonization (co-HTC) of sewage sludge (SS) and coal slime (CS) were investigated. The results showed that a synergistic effect existed during the co-HTC process of SS and CS, which could make the mass yield, high heating value, carbon retention rate, energy recovery efficiency, fuel ratio, and energy balance of the hydrochar increase by 1.87–6.52%, 4.04–17.54%, 7.52–16.80%, 4.20–19.59%, 7.58–25.45%, and 35.26–40.08%, respectively. Furthermore, thermogravimetric and derivative thermogravimetry analysis indicated that the weight loss of co-hydrochar was significantly increased with increasing of CS ratio, and it was 38.39%, 48.14%, and 58.08% when the CS ratio was 25%, 50%, and 75% respectively. Adding CS during HTC could significantly improve the combustion performance of the hydrochar. Moreover, SS and CS were efficiently converted into solid fuels with better combustion performance and reactivity. [ABSTRACT FROM AUTHOR]

This work intends to evaluate the feasibility of improving the adsorption performance of biomass by both hydrothermal carbonization (HTC) pretreatment and single-step NaOH and ethanol modification. Peanut shell (PS) and pine (PE) are utilized as parent materials to produce efficient adsorbents, and malachite green (MG) is regarded as contaminants to evaluate the adsorption capacity of prepared materials. Adsorption test was performed under various operating conditions, including pH, interfering ions and contact time. The adsorbents were characterized by N2 adsorption–desorption, SEM, FT-IR spectra and elemental analysis to explore the potential adsorption mechanism. Results show that single-step NaOH and ethanol modification is an effective chemical modification to improve the adsorption performance of adsorbents by increasing the surface hydroxyl functional groups. The adsorption performance of adsorbents prepared by HTC following with chemical modification is best; the qe of modified hydrochar from PS and PE (MPS-HC and MPE-HC) reach as high as 570.34 mg/g and 562.2 mg/g, respectively. According to adsorption isothermal and kinetics analysis, the adsorption process mainly occurs on the surface of adsorbents, and MG removal is dominant by chemical adsorption resulting from the increase of surface hydroxyl functional groups by chemical modification. HTC pretreatment could enhance the п–п bond interaction, thus further promoting MG removal by MPS-HC and MPE-HC because it increases the aromaticity of hydrochar evidenced by the H/C ratio decrease. This work indicates that the combination of HTC pretreatment and chemical modification is a feasible way to improve the adsorption performance of biomass. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising technology for wet manure treatment by converting animal manure into valuable fuels, materials, and chemicals. Among other HTC process parameters, the temperature influences HTC products the most. As various animal manures have different compositions, it is not certain how the HTC temperature influences the hydrochar and HTC process liquid. To evaluate the temperature's effect on HTC, three different manures (poultry, swine, and dairy) were hydrothermally carbonized at three different temperatures (180, 220, and 260 °C), and solid and liquid products were characterized for their morphology, elemental compositions, and ions. The carbon contents of the hydrochar reached as high as 38.98 ± 0.36% and 40.05 ± 0.57% for poultry and swine manure, respectively, when these manures were treated at 260 °C. Ammonium showed an around 30% increase in poultry manure hydrochar with the increase in the HTC temperature. In contrast, in swine manure, it decreased by around 80%, and in dairy manure, the HTC temperature did not have any remarkable effect on the ammonium content. The process liquids from HTC of dairy manure at 220 °C showed the most balanced distribution of different ions, with 4970 ± 673 ppm of sodium, 4354 ± 437 ppm of ammonium, 2766 ± 417 ppm of potassium, 978 ± 82 ppm of magnesium, 953 ± 143 ppm of calcium, 3607 ± 16 ppm of chloride, and 39 ± 7 ppm of phosphate. These results emphasize the manure-specific effects of the HTC temperature on both solid and liquid products, indicating the need for optimized strategies to enhance HTC processes for various types of animal manures. [ABSTRACT FROM AUTHOR]

In this study, the removal of RhB from water by furfural residue (FR) biochar was prepared by hydrothermal carbonization (HTC) and citric acid (CA) modification and named this biochar as CHFR (C refers to citric acid, H refers to hydrothermal carbonization and FR is furfural residue). The CHFR were characterized by SEM, FT-IR and XPS, and CHFR was investigated by the effects of initial concentration, adsorbent dosage, pH, and contact time on the removal of RhB, and the experimental data were analyzed using the adsorption isotherm models, the adsorption kinetic models and thermodynamics, et al. The results showed that CHFR has strong adsorption performance, and the theoretical maximum adsorption capacity of RhB was 39.46 mg·g−1 under the reaction conditions of pH3, the dosage of 1.5 g·L−1, and 120 min contact time, with a removal efficiency close to 100%. the adsorption of RhB by CHFR is spontaneous and endothermic, which is consistent with the Freundlich adsorption, and the isotherm model fits well with the pseudo-second-order model, and the adsorption rate could still be as high as 92.74% after five regenerations, therefore, CHFR is an environmentally friendly and efficient adsorbent with excellent adsorption regeneration performance. [ABSTRACT FROM AUTHOR]

Hyperparameter tuning is crucial in the development of machine learning models. This study introduces the nonlinear shrinking factor and the Cauchy mutation mechanism to improve the Dujiangyan Irrigation System Optimization (DISO), proposing the improved Dujiangyan Irrigation System Optimization algorithm (IDISO) for hyperparameter tuning in machine learning. The optimization capabilities and convergence performance of IDISO were validated on 87 CEC2017 benchmark functions of varying dimensions and nine real-world engineering problems, demonstrating that it significantly outperforms DISO in terms of convergence speed and accuracy, and ranks first in overall performance among the seventeen advanced metaheuristic algorithms being compared. To construct a robust and generalizable prediction model for hydrochar element characteristics, this study utilized IDISO and DISO algorithms to fine-tune the parameters of the XGBoost model. The experimental results show that the IDISO-XGBoost model achieved an average prediction performance of 0.95, which represents a 4% improvement over the DISO-XGBoost model. These results indicate that the IDISO algorithm has significant potential and value in practical applications. [ABSTRACT FROM AUTHOR]