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In the chemical activation of biomass, it is a common practice to directly mix an activating agent, such as KOH, and feedstock for production of activated carbon (AC). Nevertheless, this generates AC with a high ash content and the solid–solid contact may not be sufficient. Herein, the activation of biomass (cellulose, lignin, and sawdust) with volatilized KOH at 900 °C was proposed by placing feedstock and KOH in two beds with up-down configurations. The volatilized KOH was expected to penetrate and activate the biomass in the upper bed. The results confirmed the hypothesis and a higher yield of AC was obtained from the activation with volatilized KOH than the direct activation of the mixture. The activation with volatilized KOH resulted in lignin-derived AC with a specific surface area of 652.8 m2 g−1, which was significantly higher than that from heating without an activator (262.2 m2 g−1). The activation with volatilized KOH was also effective for creating micropores in the sawdust- and cellulose-derived AC. Notably, the activation reduced residual KOH by >90% in the cellulose-derived AC, which made recycling of the unused KOH possible and remarkably reduced the cost for post-pretreatment of the AC for removing the inorganics. Besides, the activation with volatilized KOH enhanced the carbonization and thermal stability of the AC. In addition, the intensive cracking reactions in the direct activation destroyed the fibrous biological structure of the biomass in the AC, which, however, could be retained in the activation with volatilized KOH. Furthermore, the activation with volatilized KOH also showed a lower environmental impact and higher material efficiency than the direct activation. [ABSTRACT FROM AUTHOR]

In this research, an inexpensive porous carbon was synthesized by chemical activation of a thermally carbonized sawdust using KOH as an activation agent. The effect of three major process parameters—temperature, time, and KOH concentration—on the uptake of NO2 and porous carbon yield were optimized using the Box–Behnken factorial design. The optimum operating conditions suggested were at a temperature = 746.18 °C, time = 73.08 min, and KOH concentration = 6.45 mol L−1. The activated carbon synthesized at optimal conditions had a maximum BET surface area of 1460.64 m2 g−1 with NO2 uptake capacity and yield of 449.64 mg g−1 and 41.25%, respectively. Furthermore, the optimized activated carbon was analyzed using various analytical methods and the reusability of the spent activated carbon was investigated in several cycles. The study confirmed that the porous sawdust activated carbon is a promising adsorbent for the effective removal of NO2 with a competitive yield. [ABSTRACT FROM AUTHOR]

In this study, the efficiency of activated carbon (AC) synthesized from the shrimp shell plus cellulose (SS@C) was optimized toward Bisphenol A (BPA) adsorption. Low-cost, renewable, and non-toxic shrimp shells mixed with cellulose were carbonized, followed by activation via CO2 and NaHCO3 to produce SS@C-AC. The results revealed that SS@C-AC samples were a porous composite with mesoporous structures comprising a relatively high specific surface area (935.20 m2/g) with a mean pore size of around 3.8 nm and mesoporous volume of 1.83E−02 cm3/g. The influences of initial concentrations, pH values, and adsorption on BPA were investigated systematically. Isotherm model and kinetics study of the adsorption of BPA on SS@C-AC exhibited that the obtained data were in agreement with the Langmuir adsorption isotherm model while there is no difference between PFO and PSO kinetic results for BPA concentrations in the range 25–100 mg/L. The impregnation ratio of 1.5 NaHCO3 and an activation time of 90 min at 800°C were the optimum conditions under which BPA removal of 81.78% was obtained. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3), as a toxic gas, has negative impacts on human health even at low concentration, especially in narrowed spaces. In this study, activated carbon was synthesized from seaweed waste and copper was loaded on its surface (Cu/AC filter) to prepare a cost-effective NH 3 adsorbent. Pyrolysis (carbonization) temperature can significantly affect the texture properties of activated carbon, and the best activated carbon sample with BET of 1114 m2/g was obtained through pyrolysis at 500 °C followed by KOH-activation at 750 °C. Different from other lignocellulosic biomass-based activated carbons (mainly microporous structure), the prepared algae-based activated carbons mainly have a mesoporous structure (pore size: 7.0–9.0 nm). Copper-impregnation significantly changed the surface chemistry of activated carbon, thereby greatly increasing the NH 3 adsorption capacity (max: 128.6 mg/g). The adsorption performance was primarily determined by chemical adsorption (caused by copper impregnation and related inherent functional groups, including O–H, C–H, O–Si–O and SiO–H), followed by physical adsorption (caused by BET). Isotherm studies indicated that NH 3 adsorption on Cu/AC filter followed the Langmuir model, whereas the adsorption kinetics followed the pseudo-second-order model. Furthermore, the adsorption mechanism was controlled by intraparticle diffusion model with initial adsorption behavior. This can be attributed to the mesoporous structures of activated carbon, consequently dramatically improving the diffusion efficiency. In addition, the Cu/AC filter showed good regeneration performance, as it can still remain above 90 % after 5 cycles. Finally, this study demonstrated that the seaweed waste is a good precursor for activation carbon and has great potential as excellent NH 3 adsorbent for indoor air purification. • Seaweed waste was used to develop mesoporous activated carbon for NH 3 adsorption. • Copper impregnation greatly enhanced adsorption capacity via chemisorption. • Cu/AC filter can completely remove NH 3 (initial conc. 400 ppm) within 20 min. • Adsorption was mainly controlled by intraparticle diffusion model due to mesopores. • Cu/AC filter showed the highest NH 3 adsorption capacity (128.6 mg/g). [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile synthesis of stearic acid-loaded hydrophobic activated carbon is proposed. • 20 % ST-AC: surface specific area is 1655 m2/g and water contact angel is 132°. • Doping stearic acid increases the Π-Π force between toluene and AC. • Adsorption capacity of 20 % ST-AC is 545 mg/g at 0 %RH and 490 mg/g at 80 % RH. • Adsorption capacity of regenerated 20% ST-AC remains more than 94% after 5 cycles. The diminished adsorption efficiency of porous carbon for volatile organic compounds (VOCs) in high-humidity conditions poses a critical challenge that limits its widespread application. This study presents a facile method for enhancing the adsorption capacity of coffee grounds activated carbon in high-humidity environments through stearic acid modification. The incorporation of 20 % stearic acid (20 % ST-AC) significantly amplifies the saturated adsorption capacity and penetration duration of porous carbon for toluene under high-humidity conditions. Specifically, the toluene adsorption capacity improves from 230 mg/g to 498 mg/g in an 80 % relative humidity condition. However, increasing the stearic acid doping ratio beyond 20 % has a limited impact on moisture resistance while leading to micropore blockage, resulting in a significant reduction in toluene adsorption capacity. Additionally, 20 % ST-AC demonstrates excellent adsorption recycling performance over five cycles, maintaining 97 % of its original adsorption capacity. This study provides a novel perspective on the preparation of hydrophobic activated carbon, which helps to address the challenge of VOC adsorption in high-humidity flue gas environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • At 0.5 g/L biochar and 30 mg/L tetracycline, the biomass increased by 13.26 %. • Chlorella and biochar can adsorb tetracycline in water synergistically. • The carbon obtained from self-cultured Chlorella can be recycled for cultivation. • The activated carbon's specific capacitance is 233.15F/g for 1 A/g. Microalgae present a viable mechanism for purifying aquatic environments through the absorption of organic pollutants. In this paper, Chlorella protothecoides was cultured in a tetracycline environment, and biochar was added during the cultivation process. Compared with conventionally cultured Chlorella protothecoides , the addition of biochar for cultivation under a tetracycline environment increased the biomass of Chlorella protothecoides by 13.26 %. Moreover, the adsorption of tetracycline by biochar alone was not complete, but when mixed with Chlorella protothecoides , tetracycline was completely removed, which proved the biosorption of Chlorella protothecoides for low concentrations of tetracycline. Finally, the cultured Chlorella protothecoides was used further to prepare electrode materials, and it was found that the specific capacitance of the material reached 233.15F/g at a current density of 1 A/g. In this study, the use of biochar and Chlorella protothecoides to jointly adsorb tetracycline is of great significance for environmental protection and microalgae cultivation. [ABSTRACT FROM AUTHOR]

Producing vanillin from lignin model compounds in an elegant and efficient manner is a focus of chemical utilization in lignocellulosic biomass. The facile synthesis of a cobalt-palladium bimetallic alloy anchored on activated carbon (Co-Pd/C), which excels in the selective oxidation of the lignin model compound 4-methylguaiacol to vanillin, is reported here. The characterization results of Co-Pd/C indicate that the catalysts enhance the catalytic efficiency by forming a cobalt-palladium alloy to modulate the number of d-band cavities and influence the O 2 adsorption. Meanwhile, the synergistic effect between the alloys causes the Co-Pd/C catalyst exhibits good activity and stability in cycling experiments. A series of controlled experiments offer insight into the mechanism of catalytic generation of vanillin from 4-methylguaiacol. This work opens a new opportunity for achieving the valuable aromatic products from lignin. [Display omitted] • Alloy synergism modulates the number of D-band cavities to influence O 2 adsorption. • Modulation of Co/Pd ratio to explore the optimal ratio for alloy formation. • Carrier size affects electrostatic attraction and influences O 2 adsorption capacity. [ABSTRACT FROM AUTHOR]

An excessive exposure to indoor toxic pollutant gases such as trimethylamine (TMA) and H 2 S is fatal to humans especially in the confined workspace. A porous carbon pollutant filter was developed using rice husk as a biomass waste. The different carbonization temperature highly affected on the surface area of ARH (activated rice husk carbon) and their performance of pollutant gas adsorption. With copper impregnation on the activated carbon (Cu/ARH), much better toxic gas adsorption was achieved in an enclosed chamber. The best performance was obtained with a Cu/ARH filter carbonized at 450 °C as it eliminated the 400 ppm of TMA in 30 min and H 2 S in 15 min. Isotherm and kinetic models were applied to understand the adsorption performance. The pseudo-second order kinetic model represented the best fit, followed by the intraparticle diffusion and Yoon-Nelson kinetic models. The H 2 S adsorbed Cu/ARH filter was successfully regenerated whereas a TMA adsorbed Cu/ARH filter was not successfully regenerated. The current study is expected to expand the utilization of biomass waste for the indoor air purification. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) can negatively affect human health in confined spaces at even very low concentration due to its strong toxicity. In this work, coffee residue was used to prepare the activated carbon, then was further developed into a copper-impregnated activated carbon filter (Cu/AC) for H 2 S adsorption. The carbonization temperature has a great influence on the texture characteristics of activated carbon. The optimal activated carbon (BET: 1422 m2/g, V total : 0.655 cm3/g) was achieved at 450 ℃ carbonization and at 750 ℃ KOH-activation. Copper catalyst greatly altered the surface properties of activated carbon by producing a lot of functional groups. The Cu/AC filter showed good H 2 S adsorption performance (max adsorption capacity: 132.22 mg/g) as it can completely remove H 2 S with an initial concentration of 400 ppm in a 0.1 m3 chamber within 10 min. The adsorption capacity depended not only on BET surface area, but also on the metal catalyst (copper). In addition, functional groups produced by copper-impregnation also enhanced the adsorption performance and the rate of adsorption, especially oxygen-containing functional groups (eg. O-H and C-O). The isotherm studies showed that the adsorption of H 2 S on the Cu/AC filter obeyed the Langmuir model, while the adsorption kinetics followed the pseudo-first-order and pseudo-second-order models. The adsorption mechanism is governed by initial film diffusion and subsequent intraparticle diffusion. Furthermore, the Cu/AC filter had excellent regeneration and reusability (still maintained >95% remove efficiency after 5 cycles). Finally, the current study suggested that coffee residue is good activated carbon precursor and can be used as an excellent adsorbent for H 2 S in confined spaces. • Coffee residue was used to develop activated carbon filter for H 2 S adsorption. • Copper greatly improved adsorption capacity via surface chemistry modification. • Cu/AC filter can completely remove H 2 S (initial conc. 400 ppm) within 10 min. • Cu/AC-450 filter showed the highest H 2 S adsorption capacity (132.22 mg/g). [ABSTRACT FROM AUTHOR]

[Display omitted] • KOH was impregnated on rice husk KOH-activated carbon, named as DKOH-AC. • DKOH-AC involved both chemi- and physi-sorption when KOH-AC allowed physi-sorption. • CO 2 adsorption on DKOH-AC followed Freundlich and pseudo second order models. • DKOH-AC adsorbed 2.1 mmol/g in an indoor condition. Relatively high indoor CO 2 concentration (greater than 1000 ppm) has a negative impact on human health. In this work, a cost-effective CO 2 adsorbent (DKOH-AC) was developed by impregnating KOH on rice husk-based KOH activated carbon (KOH-AC, 1439 m2/g). KOH can be successfully loaded on the surface of KOH-AC and significantly changed its surface properties. DKOH-AC still remained a considerable surface area (206 m2/g) and showed a similar S micro /S BET ratio. In-situ FTIR analysis confirmed that the major CO 2 adsorption mechanism of KOH-AC was based on physisorption while that on DKOH-AC involved both chemisorption and physisorption. DKOH-AC showed a higher heat of adsorption (34 ∼ 41 KJ/mol) and gas selectivity (16.6) than these of KOH-AC. KOH-AC quickly reached an adsorption equilibrium (about 50 min) as compared to that of DKOH-AC. In addition, DKOH-AC exhibited an excellent adsorption performance of 2.1 mmol/g for a low concentration of CO 2 (2000 ppm ∼ 500 ppm) under indoor conditions. Both the CO 2 adsorption isotherm on KOH-AC and DKOH-AC well followed the Langmuir and Freundlich models. The CO 2 adsorption kinetics on KOH-AC followed the pseudo-first order model whereas that on DKOH-AC obeyed the pseudo-second order model. The adsorption process was controlled by the intraparticle diffusion combined with the film diffusion model. [ABSTRACT FROM AUTHOR]

• Activated carbon filter derived from peanut shell with KOH activation was utilized for H 2 S removal. • Carbonization temperature significantly affected the texture properties of activated carbon. • Max H 2 S adsorption capacity was 98 mg/g using the best activated carbon filter (S BET = 1523 m2/g). • Adsorption of H 2 S followed Langmuir isotherm model and Pseudo-first order kinetic model. • Regeneration of used activated carbon filter through heating under argon was available. Hydrogen sulfide (H 2 S), as a major air pollutant, poses a serious threat to people's health, especially in confined spaces. In this study, a porous carbon filter was developed by impregnating a copper on activated carbon derived from peanut shell biomass. The carbonization temperature can significantly affect the texture properties of activated carbon, and the optimized temperature was 450 ℃. The optimal activated carbon sample (S BET = 1523.2 m2/g, V micro = 0.533 cm3/g) was prepared at a carbonization temperature of 450℃ and KOH activation at 750 ℃. The best adsorption performance was obtained with a copper impregnated optimal activated carbon (Cu/PAC-450) filter, and the maximum adsorption capacity was found to be 97.63 mg/g. As the initial concentration of H 2 S increased, the adsorption efficiency decreased. Adsorption isotherm and kinetic studies showed that Langmuir isotherm model was the best-fitted model for the adsorption of H 2 S on Cu/PAC-450 filter, with a correlation coefficient of 0.9627. The adsorption kinetic process followed the pseudo first order model, and the adsorption mechanism was controlled by intraparticle diffusion along with film diffusion model. The used Cu/PAC-450 filter can be successfully regenerated, which showed good reusability. The Cu/PAC-450 has a very broad prospect for use in household appliances (such as refrigerator, air conditioner, microwave oven, etc.) for indoor air purification. Therefore, this study is expected to expand the utilization of agriculture waste for the indoor air purification. [ABSTRACT FROM AUTHOR]

Excessive exposure to hydrogen sulfide (H2S) and acetic acid (CH3COOH) gases is extremely dangerous in a confined space. An effective indoor air pollutant removal porous carbon filter was developed using NaOH impregnated on activated carbon (NaOH/AC) for the adsorption of H2S and CH3COOH. Activated carbon (NaOH/AC) filter was characterized using various methods, indicating good physical and chemical properties (especially ‐OH functional groups) for the adsorption of air pollutants. The prepared NaOH/AC filter was cured at different curing temperatures and residence times to understand the effect of the curing conditions on the adsorption performance. The best results were obtained with NaOH/AC filter cured at 100°C for 20 minutes as it eliminated the initial concentration of 400 ppm of CH3COOH in 15 minutes and H2S in 30 minutes at 20°C and 60% relative humidity. Isotherm and kinetic models were used to analyze the adsorption process. Langmuir isotherm and pseudo‐second order kinetic models provided the best fit to the adsorption of CH3COOH and H2S on NaOH/AC filter. The adsorption mechanism was controlled by the intraparticle diffusion combined with film diffusion. The maximum adsorption capacity of NaOH/AC filter was 473 mg/g for H2S adsorption, and 550 mg/g for CH3COOH adsorption. In addition, the spent NaOH/AC filter was regenerated for reuse. This study is expected to develop low‐cost and effective porous carbon filter using NaOH‐modified activated carbon for indoor air purification. [ABSTRACT FROM AUTHOR]

In this study, a removal technique of porous activated carbon filter was developed using copper impregnated on commercially available cocoa activated carbon (Cu/AC) for the removal of toxic pollutant gases (trimethylamine [TMA] and hydrogen sulfide [H2S]). Cu/AC (filter) was characterized with Scanning electron microscope (SEM), Energy dispersive X‐ray spectroscopy (EDS), Thermogravimetric analysis (TGA)/Differential thermal analysis, proximate analysis, Carbon, hydrogen, nitrogen, sulfur (CHNS)/O, and Brunauer–Emmett–Teller, the results indicated the Cu/AC possesses good physical and chemical characteristics and is suitable for adsorption of air pollutants. The Cu/AC filter exhibited excellent adsorption capacity for the removal of TMA (qe = 654.8 mg/g) and H2S (qe = 220.37 mg/g). The isotherm and kinetic models were applied to analyze the adsorption properties and adsorption mechanism. Langmuir isotherm showed best fit for the adsorption of TMA and H2S, whereas the pseudo‐first‐ and second‐order kinetic models best fitted in describing the adsorption of H2S and TMA, respectively. Also, the adsorption process for the removal of TMA and H2S was controlled by the intraparticle diffusion model. The H2S‐adsorbed Cu/AC filter can be regenerated but not lasting too many cycles. Techno‐economic analysis and life‐cycle analysis (LCA) were performed at a plant scale. Production costs were ¢1.37 for cocoa AC filter and ¢10.13 for activated rice husk (ARH) filter. Also, the LCA result for during the filter production was estimated to be 2.52 kg CO2‐eq for cocoa AC filter and 4.47 kg CO2‐eq for ARH filter. This study proves the competitiveness compared to ARH filter of the previous study in the adsorption performance and the filter production cost. [ABSTRACT FROM AUTHOR]

• Copper-impregnated corncob activated carbon adsorbent was employed to remove H 2 S, NH 3 , and TMA from indoor air. • The maximum adsorption potentials of CAC adsorbent for H 2 S, NH 3 and TMA were 164.54, 190.68 and 323.56 mg g−1 respectively. • Different isotherm and kinetic models have been used to analyze the data. • After the adsorption of H 2 S, NH 3 and TMA successive regeneration of spent activated carbon was feasible. In this study, a corncob-derived activated carbon was prepared via chemical activation using potassium hydroxide as a chemical activating agent for the adsorption of H 2 S, NH 3 and trimethylamine. The activated carbon was impregnated with copper to improve its H 2 S, NH 3 and TMA adsorption performance. SEM, EDX, nitrogen adsorption-desorption, TGA/DTA, proximate and elemental analysis tests were employed to characterize the activated carbon samples. Removal efficiencies of the activated carbon samples for H 2 S, NH 3 and TMA were conducted through batch experiments. The H 2 S, NH 3 and TMA adsorption potentials of the CAC were 164.54, 190.68 and 323.56 mg g−1 respectively. The isotherm analysis results showed that the Langmuir adsorption isotherm model was the most suitable to describe the adsorption isotherm of H 2 S, NH 3 and TMA. Similarly, pseudo-second order kinetic model well explained the adsorption kinetics of NH 3 and TMA while pseudo-first order showed better fit towards the adsorption of H 2 S. The findings revealed that the copper-catalyzed corncob activated carbon is a promising and sustainable adsorbent for the removal of toxic gases from indoor areas. [ABSTRACT FROM AUTHOR]

Here, we report the extraordinary electrochemical energy storage capability of NiMoO4@NiMoO4 homogeneous hierarchical nanosheet-on-nanowire arrays (SOWAs), synthesized on nickel substrate by a two-stage hydrothermal process. Comparatively speaking, the SOWAs electrode displays superior electrochemical performances over the pure NiMoO4 nanowire arrays. Such improvements can be ascribed to the characteristic homogeneous hierarchical structure, which not only effectively increases the active surface areas for fast charge transfer, but also reduces the electrode resistance significantly by eliminating the potential barrier at the nanowire/nanosheet junction, an issue usually seen in other reported heterogeneous architectures. We further evaluate the performances of the SOWAs by constructing an asymmetric hybrid supercapacitor (ASC) with the SOWAs and activated carbon (AC). The optimized ASC shows excellent electrochemical performances with 47.2 Wh/kg in energy density of 1.38 kW/kg at 0–1.2 V. Moreover, the specific capacity retention can be as high as 91.4% after 4000 cycles, illustrating the remarkable cycling stability of the NiMoO4@NiMoO4//AC ASC device. Our results show that this unique NiMoO4@NiMoO4 SOWA has great prospects for future energy storage applications. [ABSTRACT FROM AUTHOR]

Biochar synthesized from algal biomasses acts as an efficient adsorbent to remove tetracycline (TC) from aqueous solutions. In this study, a mixture of Enteromorpha (EN) and Chlorella vulgaris (CV) was pyrolyzed at 500 °C, then activated with NaOH at 800 °C to prepare composite biochar (EC A -B). The effects of TC concentration (50–500 mg·L−1), pH (3–11), temperature (30 °C–50 °C), and contact time (0–960 min) on TC absorption were investigated. Results revealed that in aqueous solutions, the biochar (EC 4:1 -0.5)prepared with CV and EN at the mass ratio of 4:1 and the impregnation ratio of 0.5 had the optimal TC adsorption capacity (Q m = 376.878 mg·g−1). The removal rate of EC 4:1 -0.5 remained above 80 % after five cycles. The surface area of EC 4:1 -0.5 (583.329 m2·g−1) increased by three and four times that of EN and CV, respectively. Intraparticle diffusion was considered as the major limitation for the adsorption of TC onto EC 4:1 -0.5. This investigation provides a method for the synthesis and optimization of algal biomass-based activated carbon for the absorption of organic pollutants in wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

Biomass based active adsorbent can be prepared by activation process to adsorb dyes. In this study, using macroalgae as raw material, the biomass based activated carbon material was prepared by NaOH activation method to adsorb methylene blue. The activated adsorbent with high specific surface area (1238.491 m2 g−1) was characterized by BET, XRD, FTIR and XPS. The effects of impregnation ratio, amount of adsorbent, pH and contact time on the adsorption activity of biochar on MB were evaluated. The adsorption kinetics, molecular dynamics and density functional theory were discussed. The maximum MB removal efficiency of SWAC reached 98.56 % at 30 °C and pH = 5 which is due to its large specific surface area and mesoporous slit structure. MD simulation shows that MB molecules were adsorbed on carbon layer through face-to-face stacking. DFT calculation and subsequent electron structure analysis suggested that a synergistic effect of π-π stacking, cation-π interaction, and electrostatic interaction could help stabilize adsorbed MB molecules. And an excellent adsorption capacity SWAC is due to its graphitic N sites for high electronegativity. [ABSTRACT FROM AUTHOR]

Pyrolysis of biomass generates abundance of steam in volatiles, which might be used for activation of biochar to produce activated carbon for recovering the heat carried by steam and for making full use of steam. Hence, the volatiles from pyrolysis of dry and wet tomato leaves in an upper bed at 500 °C on activation of sawdust-derived biochar in the lower-bed at 700 and 800 °C were investigated. The results showed that the volatiles from the pyrolysis of dry tomato leaves reacted with the sawdust-derived biochar via polymerization/condensation reactions, forming substantial amount of carbonaceous deposit. This reduced specific surface area of the lower-bed biochar from 308 to 0.8 m2 g−1, as solid deposits from the volatile-char interaction filled majority of the pores. In converse, the abundance of water generated from pyrolysis of wet leaves facilitated gasification of the carbonaceous deposit and created more micropores. The overall specific surface area also increased to 361 m2 g−1 at 800 °C, owing to dominance of gasification but not volatile-char interactions. This rendered the biochar with higher capability for adsorption of phenol. The volatile-char interactions made the biochar oxygen-rich, more hydrophilic but thermally more stable via forming ether bridge bonds connecting benzene rings in skeleton of biochar. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Derivatives of cellulose/lignin interact in HTC, pyrolysis and activation. • Co-HTC lowers hydrochar yield as acids formed aid depolymerization. • Cross-polymerization of volatiles-biochar forms more π-conjugated organics. • Volatiles-char interaction creates additional pores in co-activation. • Interactions impact functionality, hydrophobicity and morphologies of the chars. Cellulose and lignin co-exist in agroforestry biomasses and their distinct structures lead to the formation of varied derivatives in their thermal conversions. This might induce interaction of these derivatives and shape the properties of resulting products. In this study, potential interaction of the derivatives from cellulose and lignin was investigated in three scenarios: hydrothermal carbonization (HTC) at 250 °C, pyrolysis at 550 °C and activation with CO 2 at 800 °C. The results indicated interactions among volatiles and between volatiles and char, influencing properties of varied chars. The co-HTC of cellulose/lignin reduced the yield of hydrochar, due to the enhanced depolymerization of feedstocks and heavy organics with the aid of carboxylic acids derived from cellulose. In converse, cross-polymerization reaction between volatiles and biochar in pyrolysis/activation formed additional carbonaceous solids, increasing the yield of biochar (by 5.5%) and activated carbon (by 12.4%) as well as large π-conjugated organics in the bio-oils. Aromatization reaction was enhanced during the co-pyrolysis of lignin/cellulose, making the biochar thermally more stable, while co-activation of mixture significantly increased the specific surface area of resulting activated carbon (889.0 m2g−1 versus 691.5 m2g−1 in theoretical average), as the volatiles of varied origins involved in activation of the biochar. Additionally, the co-HTC, co-pyrolysis and co-activation also significantly affected evolution of functionalities, hydrophobicity and morphologies of the hydrochar/biochar/activated carbon. [ABSTRACT FROM AUTHOR]

Volatile-char interaction has been well documented in co-pyrolysis of varied feedstocks, which might also exist in activation process and impact pore evolution of activated carbon (AC). This was investigated herein in activation of mixed sawdust and spirulina with K 2 C 2 O 4 at 800 °C in two scenarios: one-step direct activation or two-step activation with an intermediate pre‑carbonization. The results showed that volatile-char interaction via cross-polymerisation of the volatiles was more significant in the pre‑carbonization step, forming more biochar/bio-oil while less gases. However, volatile-char interaction was not that important in impacting product yields and evolution of pore structures of AC in activation. This was due to the dominance of gasification/cracking with presence of K 2 C 2 O 4 , minimizing the chances for volatile-char interaction. The in-situ DRIFTS characterization of the activation process showed that removal of oxygen-containing species like C O with K 2 C 2 O 4 was important for generating pore structures. Comparing with two-step activation, one-step activation of sawdust, spirulina and their mixture without pre‑carbonization all generated the ACs of more developed pore structures and showed higher environmental impact. The pre‑carbonization removed a significant portion of thermally unstable aliphatic structures, enhancing aromatic degree and creating difficulty for generating pores via gasification/cracking in subsequent activation. [Display omitted] • Volatile-char interaction in pre‑carbonization forms more biochar while less gases. • Dominance of gasification/cracking weakens volatile-char interaction on activation. • Abundant aliphatic structures develop more pores in direct activation of feedstock. • Pre‑carbonization enhance aromatic degree, negatively impacting pore development. • Activation with K 2 C 2 O 4 cracks O-containing species, suppressing aromatization. [ABSTRACT FROM AUTHOR]

CO 2 and H 2 O are two important activators in production of activated carbon (AC) via physical activation method. They could oxidize the carbonaceous species in biochar or biomass via varied mechanisms and might also impact environments as well as the pore structures and evolution of functionalities of AC in different ways. In this study, the activations of the biochar from pyrolysis of cellulose with H 2 O, CO 2 or mixed H 2 O/CO 2 were performed. The results demonstrated that H 2 O as an activator led to higher weight loss than that of CO 2 during the activation, originating from its higher efficiency for oxidation of the aliphatic structures in biochar to –OH and their further removal via deoxygenation or dehydration. Activation with CO 2 made the AC more oxygen-rich, due to the retainment of abundant oxygen-containing functionalities, which suppressed further oxidation of carbon species and led to formation of main micropores. The higher capability of H 2 O for deoxygenation made the AC more carbon-rich with much more developed pore structures as well as higher proportion of mesopores and thus the superior capability for adsorption of phenol. In addition, during the activation in either CO 2 or H 2 O, the unsaturated aldehyde/ketone and C-O-C structures was thermally more stable than lactones, saturated aliphatic acids and aliphatic aldehydes. The life cycle analysis (LCA) suggested that CO 2 activation showed lower impact on environment by reducing emissions and consumption of fossil fuel. [Display omitted] • Carbon yield is lower in activation of biochar from cellulose in H 2 O than in CO 2. • CO 2 makes activated carbon (AC) O-rich, due to lower capability for deoxygenation. • AC obtained with H 2 O has more developed pore structure of mesopores than with CO 2. • C C–C O and C–O–C on AC are more stable than saturated lactones/acids/aldehydes. • LCA indicates that CO 2 activation shows lower impact on environment. [ABSTRACT FROM AUTHOR]

• CO 2 removal and methane enrichment of biogas by adsorption of gas molecules to solid surfaces of sorbents was reviewed. • With 15 g of calcium hydroxide at a temperature around 220 °C a purity of 99.9 % of methane is reached. • Using AC methane adsorption passed from 73 % for 15 g to 86 % for 30 g. • For 30 g of AC plus 1 wt% amines, the maximum amount of methane concentration was equal to 87 % • Biomethane production cost is estimated at around 0.15 €/Nm3 An important percentage of biogas is made of CO 2 , which decreases its heating value. If CO 2 is adsorbed two advantages can be achieved: CO 2 capture and the increase of biogas heating value. Biomethane is a renewable fuel, which can provide energy autonomy and a reduction of greenhouse gases emissions. CO 2 capture from power plants by using solid adsorbents is an effective method for the reduction of CO 2 emission and an excellent solution for methane enrichment of biogas. This work evaluates the CO 2 removal and methane enrichment of biogas by adsorption of gas molecules to solid surfaces of sorbents in a pilot-scale biogas upgrading system. The materials selected to remove CO 2 from gases were three: calcium hydroxide, commercial activated carbon and solid amine adsorbent, loaded on commercial activated carbon. The amine adsorbent used in this work was polyethylenimine (PEI). The adsorbents were characterized by thermal stability through thermogravimetric analyzer (TGA), X-ray diffraction analysis (XRD), specific area, pore size distribution and particle size distribution. The CO 2 adsorption capacities of the sorbents were measured using a thermogravimetric analyzer with pure CO 2 at atmospheric pressure. The CO 2 adsorption capacity test was 0.00653 mol/g for calcium hydroxide, 0.00219 mol/g for commercial activated carbon with 0,1 wt% of amine and 0.00168 mol/g for commercial activated carbon. The effect of adsorbent dosage as a function of time was also investigated. The result showed that the CO 2 adsorption of the sorbents increases with adsorbent dosage. The results obtained from the upgrading tests conducted in the lab-scale system showed that a purity of 99.9 % methane was obtained using 15 g of calcium hydroxide, a purity of methane of 87 % was obtained using 30 g of commercial activated carbon with 0.1 wt% amine and a purity around 86 % methane was obtained using 30 g of commercial activated carbon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reactions of volatile and biochar fill pores via forming carbon deposit on biochar. • Aliphatic of cellulose are more reactive than phenolics of lignin with biochar. • Volatile-char interaction consumes aldehydes/ketones and π-conjugated organics. • Volatile-char interaction dominate pore formation instead of activation with H 2 O/CO 2. • Interaction aids deoxygenation, forming C-rich biochar of higher energy yield. CO 2 and H 2 O are commonly used oxidants for activation of carbonaceous feedstock, which are also major products in biomass pyrolysis. The heated CO 2 and H 2 O from pyrolysis might be used directly to activate biochar without cooling down. This was investigated in a reactor with dual fixed beds with biochar on the bottom and biomass feedstock (poplar sawdust, cellulose, or lignin) of the same origin on top. The CO 2 and H 2 O together with the volatiles generated at 700 °C from the top bed passed through the lower-bed biochar for activation. The results indicated that, except for CO 2 and H 2 O, the volatiles from pyrolysis of upper-bed biomass were highly reactive with the lower-bed biochar, especially for the cellulose-derived aliphatic volatiles. This formed carbonaceous deposit and enhanced the yield of biochar at expense of the volatiles (i.e. aldehydes/ketones and heavy organics of large π-conjugated structures), leading to lower yields of bio-oil. The carbonaceous deposit formed via cracking and/or polymerization filled the pores and substantially decreased the surface specific area by 99.9 % for sawdust-biochar, 87.4 % for cellulose-biochar, and 33.1 % for lignin-biochar. The volatile-char interaction, instead of the activation with CO 2 and H 2 O, dominated the pore development of biochar. Additionally, the interaction of volatiles with biochar enhanced deoxygenation, producing the carbon-rich biochar of higher heating value and energy yield. [ABSTRACT FROM AUTHOR]

Activated carbons synthesized from biomass (agricultural and food wastes) are considered promising materials for adsorbing organic pollutants. In this study, the mixture of shrimp shell (SS) and cellulose (C) were used as precursors for the synthesis of activated carbon (SS@C) with high surface area, well-developed pore structure and stable structure. On this basis, the magnetic adsorption material was prepared through NaHCO 3 activation and Fe 3 O 4 precipitation. Mean pore diameter (nm), surface area (m2·g−1), and micropore size (cm3·g−1) of SS@C.AC-M were characterized by SEM-EDS and N 2 sorption analyses. The characterization of SS@C.AC-M revealed that the optimal mass ratio of SS@C and NaHCO 3 was 1:1.5. In the absorption of Bisphenol A (BPA), the synergistic effects of BPA concentration, pH, and retention time were analyzed by response surface methodology (RSM). A pseudo-second-order model was proposed, which revealed the maximum adsorption capacity of the BPA onto SS@C.AC-M was 207.77 mg g−1. To test the reusability of SS@C.AC-M adsorbent, 5 cycles of pollutant removal experiments were carried out. This work provides a synthesis and optimization method of biomass-based activated carbons for the absorption of organic pollutants in wastewater. • A porous and stable activated carbon is synthesized by shrimp shell and cellulose. • The adsorption capacity of Bisphenol A onto SS@C/AC-M is investigated. • The reusability of SS@C/AC-M adsorbent is certified by cyclic adsorption test. [ABSTRACT FROM AUTHOR]

A new mathematical model was proposed to predict in-duct mercury capture efficiency and determine the effect of sorbent properties on mercury capture by sorbent injection. The model was based on external film mass transfer assumption and included mass balance and adsorption isotherm. Adsorption parameters of the sorbent were determined by the fixed-bed mercury adsorption experiments and other modeling parameters were estimated from literatures. The model verification was conducted by comparing with the experimental results of mercury capture by raw and bromine modified activated carbon (R-AC and AC-Br) injection in an entrained flow reactor. The results show that there is a reasonable agreement between the modeling prediction and the experimental results, which demonstrates that this model can provide a rational prediction results and be used to estimate sorbent consumption cost. In both the experimental and modeling cases, mercury capture efficiencies are improved with smaller sorbent particle size, longer sorbent residence time and larger sorbent concentration. The in-duct mercury capture rate of AC-Br was improved significantly compared to that of R-AC. The simulation of in-duct mercury capture by sorbent injection demands taking into account the additional mercury capture by deposited activated carbon on the duct wall. The model parameters, including sorbent concentration, particle size, equilibrium constant K , external film mass transfer coefficient and residence time have important effects on the in-duct mercury capture rate by sorbent injection. [ABSTRACT FROM AUTHOR]