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Heavy metal contamination has been one of the primary environmental concerns for many years in most developing countries. As the industries continue to search for low-cost and efficient adsorbents to treat their effluents contaminated with these toxic metal ions, biomass-based adsorbents have gained much attention. This work exploits such ten different biomass-based adsorbents (namely, Karanja de-oiled cake, Neem de-oiled cake, Neem leaves, Moringa Leaves, Bagasse, Mango Kernel, Wheat Bran, Eucalyptus, Fly ash, and Corn cob) for adsorption of copper ions in particular. Further, selected adsorbents (namely Karanja de-oiled cake, Neem de-oiled cake, Bagasse, Wheat Bran and Mango Kernel) were taken to the next stage and modified to biochar and tested again for copper removal. Among the biomass-based adsorbents, the highest adsorption capacity was observed for Neem de-oiled cake (equal to 9.6 mg/g). While for biochar-based adsorbents, Bagasse showed the highest adsorption capacity for copper (equivalent to 13.0 mg/g).

In this work, performance of laboratory-synthesized dolochar has been investigated for adsorption of Cd2+ ions in a large-scale process with the application of Aspen Adsorption. Moreover, the optimum values of the operating parameters (namely, flow rate, bed height, and inlet metal ion concentration) that would result into maximum amount of cadmium ion adsorption (high exhaustion capacity) in minimum time (less exhaustion time) for a fixed mass of dolochar have been calculated via the application of response surface methodology. It was found that, at optimum values of bed height (3.48 m), flow rate (76.31 m3/day), and inlet concentration (10 ppm), the optimized value of exhaustion capacity and exhaustion time for cadmium ion adsorption in dolochar packed bed is equal to 1.85 mg/g and 11.39 h, respectively. The validity of these simulation experiments can be proven by the fact that the obtained exhaustion capacity of dolochar packed bed always remained in close proximity of the experimentally obtained value of adsorption capacity of the dolochar in batch process mode (equal to 2.1 mg/g).

Zeolites and metal-organic frameworks (MOFs) are popular adsorbents when it comes to capturing CO2 from the gaseous feed stream. In this study, a hybrid of zeolite and ZIF-8 adsorbent was synthesized from coal fly ash via fusion-hydrothermal process and then in-situ aqueous ZIF-8 synthesis technique. This technique of in-situ synthesis is highly cost-effective as it is done at room temperature. The hybrid adsorbent showed an enhanced microporosity as compared to zeolites synthesized from coal fly ash due to the in-situ synthesis of ZIF-8 upon coal fly ash zeolite. It was designated as CFAZ/ZIF-8. At 298 K, a maximum CO2 uptake value of 2.83 mmol/g was observed with a constant decrease with an increase in temperature. BET surface area value of 426 m2/g was obtained for this adsorbent. Kinetics fit for the best uptake value was performed with the Avrami model kinetics, describing the adsorption well at an R2 value of 0.997 for the fit. The adsorbent also showed impressive cyclic stability after five cycles of carbonation and decarbonation. The cyclic stability studies show that the as-synthesized hybrid adsorbent shows promise in CO2 uptake studies.

Nanomaterial adsorbents are highly favorable for heavy metal removal due to their large specific surface areas with enhanced active sites for contaminant adsorption. This paper focuses on nanomaterial adsorbents covering aspects like methods of synthesis, types of nanomaterials, kinetics, process optimization, modelling and simulation and column studies besides citing future challenges. It has been found that among various synthesis protocols, Chemical Vapor Deposition was most effective in giving desired attributes. Metallic composites and organic nanomaterials viz., nanocellulose, carbon nanotubes, graphene complexes, magnetite forms etc exhibited highest metal removal capacities of 1989 mg/g for Hg (II) 1641 mg/g for Cd (II) at optimal process conditions. Eco-friendly nanomaterial adsorbents, their properties and potential are also discussed in detail. This work also explores the performance of nanomaterials in fixed bed columns where it showed its capability to be used as an effective adsorbent in continuous adsorption mode.

The increasing demands of efficient and sustainable energy generation methods from waste products have taken a giant leap in the last century, and especially in the previous two decades. Wastewater treatment has also been a much-researched topic in recent years owing to the exponential increase in effluent-laden wastewater from industries, the agricultural sector and food sector, and its effects on the environment. There have been plenty of wastewater treatment techniques over the years, but most of them lack in terms of cost-effectiveness, durability, and energy recovery rates. Microbial fuel cells can prove to be of great use to tackle both of these issues in one go, as they perform bioelectrochemical processes on organic biodegradable compounds to oxidize them to generate power which can be harnessed by various means. This article explains the aim, construction, mechanism, and application of microbial fuel cells; the economic and scientific challenges that they face in the future; and microbial fuel cell (MFC) hybrid systems which make use of MFCs combined with other useful technologies for greater aims and better efficiencies. It overall discusses the various ways in which MFCs outperform other wastewater treatment technologies by significantly decreasing sludge production and being environment-friendly, and also some limitations and drawbacks that MFCs face owing to the fact that they are relatively newer technologies and still require decades of modifications until they reach excellent output rates. MFCs are known not only for wastewater treatment but also for contaminant removal, heavy metal removal, biohydrogen production, applications in biosensors, etc., as also discussed in this article.

NiO–MgO nanocomposites are synthesized using solution combustion, sonochemical, and co-precipitation synthesis to understand the catalytic activity of CO2 methanation. Excellent particle size distribution was noticed with the sonochemical routed synthesis method, and the CO2 conversions are found to be better with the same synthesis protocol. Surface modifications in NiO–MgO composite were incorporated by doping M (M = Co, Fe, and Cu). The active catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand physical, structural properties and surface morphology of the nanocomposites. All catalysts showed excellent catalytic activity for the conversion of CO2 to methane and selectivity towards methane to be higher than 85%. However, 2%Co/NiO–MgO showed the lowest activation energy of about 43 ± 2 kJ mol−1 among other synthesized catalysts. The mechanism of CO2 methanation was investigated with the inputs from temperature programming reduction with H2 (H2-TPR), and temperature programming desorption with CO2 (CO2-TPD) studies. Detailed reaction mechanism and kinetics are investigated for all doped catalysts. M/NiO–MgO offered excellent stability up to 50 h reaction time with high CO2 conversions and CH4 selectivities.

Transition metal (Ni, Cu and Fe) substituted Co3O4–ZrO2 catalysts (NiCZ, CuCZ and FeCZ, respectively) were synthesized by PEG assisted sonochemical synthesis and tested for lean methane combustion. These catalysts offered complete combustion of methane by generating CO2 and steam as products. The strong metal-support interaction (SMSI) allowed the high catalytic activity at temperatures below 600 °C. All catalysts have shown superior stability for 20 h of time on stream conditions. In practical conditions, SO2 presence is obvious in methane feed, even trace levels of it inhibits the catalytic activity to a greater extent. In this study, the performance of catalysts and reaction mechanism was evaluated in presence of SO2 in reactant feed using packed bed catalytic activity studies and in situ FTIR. Among all catalysts, FeCZ has shown superior catalytic activity even under SO2 in the feed compared to NiCZ and CuCZ. The apparent activation energy was found to be larger in case of SO2 presence for all the catalysts. The structural and reducibility properties have been characterized with the XRD, XPS, TEM and H2–TPR studies.

A Cu-BTC (MOF-199) [copper(II)-benzene-1,3,5-tricarboxylate] catalyst has been synthesized and evaluated for imine synthesis from amine compounds under neat conditions. The performance of the Cu-BTC MOF was significantly higher than that of the CuO supported on Al2O3, TiO2 and SiO2 catalysts. The role of surface Lewis acid sites on the catalyst in the formation of imine products was illustrated by the pyridine-IR studies. The recovered Cu-BTC catalyst demonstrated consistent activity for five cycles under similar experimental conditions. The physicochemical properties of the catalysts were analyzed by XRD, BET-SA, FT-IR, UV-DRS, SEM, TEM, XPS and pyridine adsorbed DRIFT spectroscopy.

Enhancing the flow rate by reducing the drag in turbulent flows of fluids is a highly significant phenomenon with reference to many industries viz., oil, marine, irrigation, biomedical etc to reduce power consumption. This drag reduction could be mostly achieved by adding polymeric additives, also referred to as drag reducing agents (DRAs) to the fluid in trace amounts. In this study, pressure driven set-up with pipes of different diameters and roughness levels has been employed to study drag reduction by polymers like PEO, PAM, PAA, HPMC in water systems. The objective of the work was to identify the optimum set of process parameters in terms of polymer nature and its concentration, pipe diameter and its roughness, methodology adopted to maximize maximum drag reduction. The results achieved were then validated with well proven concepts and reported studies.

This work is aimed to study the effect of various processes and design parameters viz., binder concentration, binder composition, spray rate and spray gun location on the granule and tablet attributes of Lactose-MCC mixture employing a process intensified fluid bed granulator. Experiments were designed so as to understand the complex interplay of various parameters at micro level on different attributes like attrition strength, Carr’s index, Hausner ratio, Granule Size distribution etc. The effect of viscosity and droplet size of the binder estimated using well established models was studied on the above said attributes. The results achieved were interesting that point new directions to granulation research.

Over the years, researchers have continuously searched for ways to achieve adsorption of heavy metal ions from the industrial effluents at lowest possible cost, which has resulted into the development of innumerous special type of low cost adsorbents, called biosorbents. While potential of many biosorbents have been explored in laboratory setup, very few studies have tried to scale up the biosorption process and predict the performance of these biosorbents in a large scale industrial setup. In this work, performance of laboratory synthesized dolochar has been investigated for adsorption of Cd2+ ions in a large scale process with the application of Aspen Adsorption. Moreover, the optimum values of the operating parameters (namely, flow rate, bed height and inlet metal ion concentration) that would result into maximum amount of cadmium ion adsorption (high exhaustion capacity) in minimum time (less exhaustion time) for a fixed mass of dolochar (1200 kg) have been calculated via the application of Response Surface Methodology. It was found out that, at optimum values of bed height (3.48 m), flow rate (76.31 m3/day) and inlet concentration (10 ppm), the optimized value of exhaustion capacity and exhaustion time for cadmium ion adsorption in dolochar packed bed is equal to 1.85 mg/g and 11.39 hours, respectively. The validity of these simulation experiments can be proven by the fact that the obtained exhaustion capacity of dolochar packed beds always remained in close proximity of the experimentally obtained value of adsorption capacity of the dolochar in batch process mode (equal to 2.1 mg/g).

Global warming has been a serious concern worldwide. Greenhouse gases like CO2 majorly contribute to the rise in average global temperature. Attempts have been made to reduce the CO2 in the atmosphere. However, carbon capture alone was not found to be commercially viable. Various other green and cost-effective methods to convert CO2 into more useful products have been researched. CO2 methanation was found to be one such vital reaction of converting CO2 to useful fuel, like methane, using different catalysts. In this paper, this vital reaction has been reviewed comprehensively. Studies conducted with respect to materials that have proven catalysts such as Ni, synthesised by impregnation, to be the most suitable, where use of promotors (like Si and Ce) and supports (like zeolites, ceria and MOFs), high pressures, low humidity and optimum temperatures have led to increased selectivity, have been presented. The different reactors/contactors that have been used in this process at various scales, their design parameters, process conditions, performance, and limitations have been discussed which have shown the use of annular fixed bed reactors to be the most favourable. The different mechanisms proposed for the reaction, involving various intermediates, mainly carbenes and formates, and problems incurred in low temperature operation and finding of an appropriate support and promotor have been presented. Thermo-kinetic modelling studies on this reaction have also been presented and discussed. Every section has been summarized in the form of a table. The recent advances as well as future challenges and prospects of the above-said aspects of CO2 methanation have also been cited. Recent advances suggest methods of electrocatalytic reduction potentially employing Cu based compounds and perovskite oxides as catalysts, bio-electrocatalytic reduction using microbes as catalysts, and photocatalytic reduction using noble or critical metals including Ni and TiO2 as catalysts and graphene as a support, for the conversion of carbon dioxide to methane.

Chitosan, a low cost polymer, has been used in many studies for adsorption of heavy metal ions. This review covers the performance of all those adsorbents which were derived from chitosan for the adsorption of heavy metal ions in recent past. Further, the common chitosan modifications methods have been discussed in this paper among which crosslinking and grafting were found to be the most popular methods. Adsorption equilibrium and kinetics were also studied and Pseudo-second order kinetic model and Langmuir isotherm were found to be successful for modeling of most of the chitosan derivatives-metal adsorption experiments. Moreover, with focus on chitosan derivatives, effect of adsorbent structure on metal removal, adsorption mechanism, effect of co-existing ions on adsorption, adsorbent synthesis protocols and regeneration methods have been also discussed in great detail. Finally, fixed bed column design for industrial wastewater treatment was elaborated along with efficiency of chitosan based adsorbents in columns.

This work analyzes the pressure driven flow of a power law fluid in a slit microchannel of asymmetric walls with electroviscous effects. The steady state Cauchy momentum and the Poisson-Boltzmann equation are solved for the velocity and the potential distribution inside the microchannel. The Debye-Huckel approximation as applicable for low zeta potentials is not made in the present work. The unknown streaming potential is solved by casting the governing equations as an optimization problem using COMSOL Multiphysics. This proposed method is very robust and can be used for a wide variety of cases. It is found that the asymmetry of the zeta potential at the two walls plays an important role on the streaming potential developed. There is a unique zeta potential ratio at which the streaming potential exhibits a maxima for both Debye-Huckel parameter and the power law index. Shear thinning fluids exhibit a stronger dependency of the streaming potential on asymmetry of the zeta potential than shear thickening fluids. For Newtonian fluids narrow slit microchannels develop larger streaming potentials compared to wider microchannels for a given asymmetry.

Hydrogen as a clean fuel is becoming vital in view of depleting fossil fuels and ever increasing energy demand. Hence hydrogen generation and storage gains immense importance. In this review article, different methods of hydrogen storage viz., physical, chemical and electrochemical in various forms like gas, liquid and solid have been discussed and compared in terms of their efficacy, capacity, operating conditions and other safety aspects. Modeling and simulation studies reported on various aspects of hydrogen storage have been presented and compared vis a vis governing equations, applications, assumptions, merits and demerits. These modeling studies would enable to understand the phenomenon better and to explore new avenues. Kinetic and thermodynamic aspects of hydrogen storage especially employing metal hydrides have been discussed too to understand the mechanism, rate controlling actors and energy aspects. Future challenges and prospects of all the aspects of the review were provided.

There exists an ever increasing demand for coal fly ash stabilized sorbents which are thermally stable up to multiple carbon capture cycles at high temperatures (up to 950 °C). The industrial scale-up of this sorbent’s regeneration is limited by its inherent kinetics and thermodynamics that need to be maneuvered carefully to make it economically viable. In this study, sorbents regeneration kinetic and thermodynamic parameters have been estimated under nonisothermal conditions using thermogravimetric analysis. The Coats and Redfern equation has been chosen to estimate thermokinetic parameters under nonisothermal conditions. The thermodynamic values of Gibbs free energy, entropy, enthalpy, etc., for the synthesized sorbent (CaO50MgO10FA-C40) were compared with the simulated values (HSC software) with and without fly ash. The experimental data of sorbent regeneration was then fit into a suitable kinetic equation, based on the classic grain model and studied at various isothermal calcination temperatures. Sor...

Polymer induced turbulent drag reduction has significant industrial importance and finds application in industries, oil and gas, fire-fighting, marine, irrigation, biomedical etc. Most of the reported literature is focused on the skin drag reduction in pipe flow employing drag reducing additives (DRAs) like polymers, surfactants, fibres and suspensions. In this work, the effect of polymeric addition on the total drag reduction (skin and form) is studied for turbulent flow of water through various fittings like 45 degree elbow, 90 degree miter, sudden expansion and sudden contraction. Different polymers like PAM, PEO, HPMC have been employed as DRAs at various concentrations and pressure drops. The results indicate a complex and interesting behavior. When compared to the results reported for pipe flow, even in this case polymers are found to give total drag reduction (TDR) though less relative to skin drag alone. The extent of TDR is found to depend on the nature of fitting, polymer and its concentration and the pressure drop used. From the results, it is also clear that there is a strong need to further investigate the problem using sophisticated analytical tools on rheometry and polymer degradation.

Forward osmosis as a water treatment option has been extensively studied in recent decades owing to its energy efficiency and enhanced performance. Even hybrid options of integrating forward osmosis with other separation technologies have been explored. In this article, forward osmosis has been comprehensively reviewed with reference to various process and engineering aspects viz., membranes, membrane fouling, contactors and their design, draw solutions, integration of forward osmosis with various other separation technologies and modeling, and simulation. Every aspect has been thoroughly reviewed and discussed in terms of development trends, in addition to presenting the future challenges and prospects.

A thorough report is provided in this review on Molecular Dynamics (MD) simulations of polyamide-based materials. MD simulations have been carried out using polyamides combining with different organic, inorganic, polymeric and bio-based materials in abundance and all these have accounted systematically and segregated in concerned sections in this report. The motive of this review is to aid researchers in familiarising with software packages, force field parameters and computational mode of evaluating the required parameters. Choice of force field potentials is a major part of the computational work which affect adversely in the calculations and determine the extend of mirroring the real-world materials and procedures. The review has been divided into sections focussing on specific properties and are sequenced in the following way -physical properties, membrane study, mechanical properties and thermal properties. Physical properties encompassing density, morphology, interfacial interaction, cross-linking and many more have been reported. Under membrane study, diffusion of all three types of matter – liquid, solid, gas, have been discussed for polyamide membranes reinforced with different fillers. Mechanical aspects involving modulus, tensile strength, fatigue and wear resistance have been explored. Thermal properties mainly dealt with the thermal conductance of the polymer under testing conditions. Polyamide simulations have been carried out for nearly three decades and all the information regarding the developments and challenges are mentioned in this report.

Particle agglomeration by granulation was a very ubiquitous operation that finds applications in various industries such as pharmaceutical, food, chemical, fertilizer, etc. Among many granulators, ...

Wet granulation is a very important unit operation that finds applications in many industries mainly pharmaceutical and chemical industries. Various granulation technologies in batch and continuous modes were employed viz., high shear granulators, fluid bed granulators, twin screw granulators and the novel ones like foam granulators, steam granulators, dry granulators etc. In this review, various aspects of pharmaceutical granulation like technologies, characterization tools, process control, modelling and simulation, kinetics and scale up have been thoroughly analysed and discussed in terms of development trends and future challenges and prospects. The critical role played by various off line and inline characterization tools was highlighted along with their applications. Studies from PBM, DEM to hybrid models, CFD and ANN based models were presented in terms of their performance and challenges. Kinetic studies to understand the rate and influencing parameters of various steps involved in granulation process with controlling regimes were discussed along with the models used. The scale-up, a major challenge in granulation was also discussed in terms of the methodology and efficiency in retaining the granule attributes with proper control of process parameters was also presented. Process control protocols employed in the wet granulation process was discussed along with the relations of different granule and tablet attributes to process and design parameters. The future challenges and prospects in the above mentioned aspects were listed for prospective researchers.

Global warming and associated climate change has resulted in serious efforts towards reducing greenhouse gas emissions, primarily carbon dioxide through carbon capture. There are various technical options in pre- and post-combustion modes available viz., adsorption, absorption, membrane separation, chemical looping combustion with and without oxygen uncoupling and cryogenic separations. Among all these, absorption technology which could be deployed as a post-combustion option to be integrated with power plant, has been commercialized with amines as solvents long back. But there is a long way to go to improve this process in terms of economic viability due to large regeneration costs involved and to make it more environmental friendly with minimum toxic and corrosion problems due to solvents. In this review, absorption based carbon capture has been reviewed comprehensively and critically in terms of various aspects like solvents and their synthesis protocols, performance analysis of different solvent systems, contactors, kinetics and thermodynamics, modeling and simulation studies etc. Every section has been discussed in terms of the trends and developments observed including the contemporary status besides citing future challenges and prospects to improve the technology.

Carbon capture (CC) employing novel sorbents at high temperature is highly significant to address the serious concerns of global warming. In this work, thermodynamic and kinetic studies have been conducted on the carbonation using doped sorbents of CaO–MgO–CFA (coal fly ash). The thermodynamic estimations not only proved the feasibility and spontaneity of the reaction but also reinforced the positive role played by CFA in not only enhancing the CC but also reducing the regeneration temperatures. Regarding the kinetic studies, a model has been proposed for both the reaction and diffusion kinetic control regimes and has been validated with experimental data at optimal conditions. Various kinetic and Arrhenius parameters have been estimated and compared with the reported values. The rate constants at 650 °C and activation energies estimated for reaction and diffusion controlled regimes were 2.5 min−1, 23 kJ/mol and 0.8 min−1, 30 kJ/mol, respectively. Our values clearly indicate the enhanced rate achieved by ...

Global warming due to greenhouse gases mostly carbon dioxide has become a serious concern worldwide. Carbon capture using adsorption, absorption, chemical looping combustion, cryogenic and membrane separations has been widely studied to tackle this problem. Significant research efforts have been made in membrane based carbon capture employable in both pre- and post-combustion options as it is a simple, efficient economical and environmentally benign option. In this paper, a comprehensive review has been done on this technology with reference to various aspects viz., synthesis, characterization and performance analysis of various membrane materials, contactors and their design aspects, modeling and simulation studies and membrane wetting phenomenon. The prospects and future challenges of the membrane based carbon capture are also highlighted.

Carbon capture using various technical options, viz., adsorption, absorption, chemical looping combustion, membrane separation, and cryogenic separation in either pre- or post=combustion modes, has been found to be the effective solution to tackle a serious concern of global warming. Although adsorption has been widely employed in carbon capture as a result of its economically and environmentally benign nature, it could not be commercialized as a result of the highly energy-intensive regeneration process involved. The major challenge in carbon capture is its sustainability at a high temperature, therefore enabling an easy integration with power generation to make it commercially viable, and also in the production of hydrogen using sorption-enhanced steam reforming. In this work, various combinations of sorbents based on CaO, MgO, zeolites H-Beta and H-ZSM 5, and Al2O3 with and without doping of coal fly ash (C and F types) have been employed in carbon capture using a lab-scale fixed-bed reactor system. Af...

There is extensive literature on the use of adsorbents derived from waste to treat industrial effluents containing heavy metal ions. However, there is limited information on the use of adsorbent blends. This is applicable for treating effluents which contain a number of heavy metals, so any one single adsorbent may not be suitable for achieving high percent removal of all ions. The present work employs adsorbent blends to treat an electrochemical effluent in batch mode. This work aims to provide valuable insights on the interaction of heavy metals with the adsorbents in blends. Effluent from an electrochemical industry was treated with blends of calcium bentonite, fly ash and wheat bran in different compositions to remove heavy metal ions (Fe, Ni, Cu, As, Zn, Cd) from an aqueous effluent solution. The optimal set of conditions identified were pH, 5–7; contact time, 60–90 min; agitation speed of 200 rpm; adsorbent dosage of 1 g/50 mL; and particle size of 150–300 μ. Metal ions arsenic, zinc and cadmium were completely removed. The percentage removal of (Fe, Ni, Cu) metal ions was in the order Fe(II)(96.73%) > Ni(II)(74.03%) > Cu(II)(70.70%) at optimum conditions in a short equilibrium time of 90 min. Batch experiments were conducted to determine the factors such as adsorbent composition, temperature, pH, agitation speed, dosage, contact time and particle size affecting adsorption, and all these parameters were found to strongly influence the adsorption. Experimental data were analyzed for Langmuir and Freundlich isotherms. Langmuir isotherm shows the maximum adsorption capacities were in order Fe(II)146.1 mg/g > Ni(II) 115.9 mg/g > Cu(II) 74.5 mg/g. Freundlich parameter ‘n’ was found to be greater than 1 which showed that the adsorption is feasible for all three metals. Freundlich isotherm fit the data comparatively better, but neither of the two isotherms satisfactorily explained the adsorption, which indicated heterogeneity of adsorption. Kinetic studies were performed and analyzed for pseudo-first- and pseudo-second-order kinetics and the Weber–Morris intraparticle diffusion model. The adsorption data fit accurately to pseudo-second-order kinetic model with coefficient of correlation values greater than 0.99 for all three heavy metals. The kinetic constants were found to be $$8.49*10^{ - 3} ,5.82*10^{ - 3} ,5.27*10^{ - 3} \frac{\text{g}}{{{\text{mg}}\,\hbox{min} }}$$ for Fe(II), Ni(II) and Cu(II), respectively. From the intraparticle diffusion model, it was inferred that there were different rate-limiting steps during the duration of the adsorption process, including intraparticle diffusion and boundary layer diffusion.

The accumulation of greenhouse gases, leading to global warming necessitated the research for efficient and recyclable CO2 capture solvents. Ionic liquids (ILs) and IL-based solvents have paved the way for a new generation of highly efficient, economic, and eco-friendly CO2 capture solvents. This paper discusses the process of synthesizing different ILs and IL-based solvents, emphasizing the merits and demerits of different processes, followed by the characterization tools and techniques, and the important considerations in developing novel ILs. An extension of characterization is the screening process. Properties of synthesized ILs and IL-based solvents have been discussed in detail, along with properties of hybrid IL-based solvents. The highly tunable nature of ILs leads to a multitude of possible ILs and IL-based solvents that can be customized for specific requirements. The latter part of the paper describes various modelling and simulation techniques used to analyse and predict the CO2-IL interactions. In each section, the trends and technology used, are analysed and discussed, duly emphasizing the latest advances. The paper concludes with a discussion on the prospects and challenges in adopting ILs and IL-based solvents in CO2 capture.

Various methods have been devised to control the ever increasing CO2 emissions in the environment, in order to prevent severe climatic changes. Among these methods, adsorption have gained much interest owing to its high efficiency and low operating costs. However, efficiency of an adsorption process is highly dependent on the adsorbent used. Therefore, many different types of solid adsorbents have been tested till date for CO2 capture, among which graphene based adsorbents have gained much attention. Owing to the low cost, high specific area and excellent stability of graphene, many researchers have used graphene and its derivatives for CO2 capture in their study. In this work, the core results of these multitudinous studies have been summarized for the reader in form of tables followed by a discussion on the observed trends and comparisons between adsorbents. The highest adsorption capacity that was observed was 0.117 mol/g for a ternary junction like membrane of Graphene/Non-compact graphene/Carbon hollow fibers. Further, beside the adsorption properties, the common protocols for graphene based materials synthesis are also summarized, which is again, in the form of a table along with discussions and comparisons and it was inferred that these materials, mostly, can be processed easily. Synthesis section is followed by yet another table-discussion combination on the common tools that are used for characterization of synthesized materials. Finally, to complete the cycle of CO2 waste management, we summarize the CO2 utilization techniques focusing on the successful studies which used graphene based catalysts for the CO2 reduction into fuels or other valuable products. The results indicated that graphene/graphene based materials can be used either as viable alternative to expensive metal-based catalysts or as a support to other catalysts which results in a boost in their performance.

This review summarizes the progress made, in the field of low-cost biosorption of heavy metal ions, over the past few years. It gives a comprehensive summary of the synthesis, performance, modification and regeneration of biosorbent. The review also focused upon optimum operating parameters, isotherm and kinetic studies. Moreover, from an industrial application point of view, fixed-bed column studies have been discussed in this paper. Methods like chemical pretreatment, grafting, immobilization, etc., which improve the biosorbent properties, have been summarized. Operating parameters that affect the biosorption process such as temperature, pH, contact time, agitation speed, etc. have been studied to understand the relationship between factors and removal efficiency. For most of the studies, biosorption process was found to be endothermic, with room temperature being optimum for the process. Grafting was observed to enhance the adsorption capacity of biosorbent enormously. Biosorption process generally followed Langmuir or Freundlich isotherm, whereas mostly the best fit for kinetic model was pseudo-second-order. Desorption process was mostly carried out via acidic eluent. The performance of biosorbents was observed to be appreciable when they were packed into fixed-bed columns.

Biochar, a solid carbon-rich residue is derived from wide variety of abundantly available raw materials like forest and agricultural waste, industrial by products and waste, and municipal solid waste through pyrolysis. Besides enhancing soil fertility thereby agricultural productivity and reducing greenhouse gas emissions, biochar based sorbents are widely being employed in waste water treatment owing to their attributes viz., high porosity, large surface area, affinity towards metals, surface modifications, stability, recyclability and even safe disposal. In this comprehensive review, latest trends w.r.t. synthesis protocols, modifications, mechanisms, metal removal comparison, thermo-kinetics, mechanisms, regeneration and safe disposal methods have been presented and discussed. Synthesis through slow pyrolysis (300−700 °C, 0.01−2 °C/s), nanoscale modifications with metal oxides especially based on iron to magnetise the biochar, regeneration through acids and complexation agents are found to be highly promising. While ion exchange and electrostatic interactions are found to be common mechanisms of metal removal which in turn depends on nature of biomass, process conditions and metal, it is found that modifications and mechanisms are strongly interrelated. From our studies, biochar based sorbents gave heavy metal adsorption capacities in mg/g of 1217 (Ag), 560 (Pb), 288 (Cu), 216 (Cd), 204 (As), 130 (Cr), 58 (Ni), 48 (Hg) etc under optimal conditions. Though the nature of kinetic models and isotherms do depend on the material and process conditions, pseudo kinetic models (first and second order) along with Langmuir and Fruendlich isotherms were most widely reported. Disposal of spent biochar could be using it in construction (cement and bricks) and electronic (super-capacitors) industries besides phytoremediation.

Metal Organic Frame works (MOFs) are being widely used in carbon capture through adsorption and membrane techniques, which are yet to be commercialized. This is due to their high affinity towards acidic gases and exceptional characteristics such as crystallinity, structural stability, high surface area and flexible pore dimensions. In this review, wide range of topics viz., synthesis protocols, modifications employed to further improve their attributes, comprehensive comparison of different MOFs used in carbon capture, thermo-kinetics modelling studies, contactors and material screening. Every section has been discussed in detail in terms of developmental trends, future challenges and prospects besides summarizing in the form of comprehensive tables at a glance for the benefit of the readers. Solvo-thermal method was found to be the most effective synthesis method besides ultra-sonication and microwave assisted methods, which also gave very good crystalline structures. The copper ligand based unmodified Cu-BTC MOF gave the maximum CO2 uptake value of 9.59 mmol/g at 273 K and 1 atm. Zn(Bmic)(AT) MOF was the only species to be tested at 353 K. Alternatively, a photo-responsive MOF, Mg-IRMOF-74-III functionalized with azopyridine gave a CO2 uptake of 89 cc/g which is comparable to many of the conventional MOFs. Kinetics indicate MOF adsorption mostly follows pseudo second order reactions either along with Toth isotherms or modified Langmuir isotherms. Fixed and fluidized bed reactors perform the best in terms of carbon capture studies. Moisture affinity, active sites and crystallinity were found to be the best factors considered whilst screening of proper MOFs.

Atmospheric warming due to greenhouse gases has become a serious global concern. Extensive efforts are being made to combat this phenomenon through Carbon Capture as carbon dioxide is its major contributor. In this work, a comprehensive review has been made on various Carbon Capture methodologies including adsorption, absorption, membrane separation, Chemical Looping Combustion, cryogenic separation with focus on their process chemistry, critical process parameters, contactor configurations, kinetics, thermodynamics, process development and scale-up. The challenges at the research and development stages have also been identified so as to provide the future directions for research.