Acid/Base-treated activated carbons: characterization of functional groups and metal adsorptive properties

Influence of Tectonically Deformed Coal-Based Activated Carbon and Its Surface Modification on Methane Adsorption

A series of coal-based activated carbons (CACs) were synthesized from mylonitized fat coal, a type of tectonically deformed coal (TDC) and symbiotic primary structural coal (PSC), followed by oxidative modification. The pore structure, surface oxygen-containing functional groups, and their influence on methane adsorption by CAC as the simplified coal model were investigated by using low-temperature nitrogen adsorption, Fourier transform infrared spectroscopy, Boehm titration, and X-ray photoelectron spectroscopy. The results showed that tectonic deformation fostered smaller pores, particularly ultramicropores in TDC, dominating methane adsorption. Acid-modified TDC-based activated carbons (ACs) showed higher pore parameters and oxygen-containing functional groups than those of PSC-based ACs. Nitric acid introduced abundant carboxyl groups concurrently increasing the pore volume and specific surface area (SSA), while sulfuric acid-ammonium persulfate treatment resulted in increased lactone groups and a partial collapse/blockage of nanopores. Methane adsorption experiments confirmed the importance of micropores and revealed a significant decrease in capacity owing to increased oxygen-containing functional groups as the primary role, with pore wall corrosion playing a secondary role. Thus, the study highlights the surface effects of TDC on methane adsorption and the potential for producing high-performance methane storage materials from China's tectonic coal resources.

Effect of Mixed Morphology (Simple Cubic, Face-Centered Cubic, and Body-Centered Cubic)-Based Electrodes on the Electric Double Layer Capacitance of Supercapacitors

Supercapacitors store energy due to the formation of an electric double layer (EDL) at the interface of the electrodes and electrolyte. The present article deals with the finite element study of equilibrium electric double layer capacitance (EDLC) in the mixed morphology electrodes comprising all three fundamental crystal structures, simple cubic (SC), body-centered cubic (BCC), and face-centered cubic morphologies (FCC). Mesoporous-activated carbon forms the electrode in the supercapacitor with (C2H5)4NBF4/propylene carbonate organic electrolyte. Electrochemical interference is clearly demonstrated in the supercapacitors with the formation of the potential bands, as in the case of interference theory due to the increasing packing factor. The effects of electrode thickness varying from a wide range of 50 nm to 0.04 mm on specific EDLC have been discussed in detail. The interfacial geometry of the unit cell in contact with the electrolyte is the most important parameter determining the properties of the EDL. The critical thickness of the electrodes is 1.71 μm in all the morphologies. Polarization increases the interfacial potential and leads to EDL formation. The Stern layer specific capacitance is 167.6 μF cm-2 in all the morphologies. The maximum capacitance is in the decreasing order of interfacial geometry, as FCC > BCC > SC, dependent on the packing factor. The minimum transmittance in all the morphologies is 98.35%, with the constant figure of merit at higher electrode thickness having applications in the chip interconnects. The transient analysis shows that the interfacial current decreases with increasing polarization in the EDL. The capacitance also decreases with the increase of the scan rate.

Microplastic inhibits the sorption of trichloroethylene on modified biochar

Biochar (BC) was used to remove trichloroethylene (TCE) from soil and water phases, and BC modification changed the sorption behavior of pollutants. Microplastics are emerging pollutants in the soil and water phases. Whether microplastics can affect the sorption of TCE by modified BC is not clear. Thus, batch sorption kinetics and isotherm experiments were conducted to elucidate the sorption of TCE on BC, and BC combined with polyethylene (PE) or polystyrene (PS). The results showed that HCl and NaOH modification increased TCE sorption on BC, while HNO3 modification inhibited TCE sorption on BC. When PE/PS and BC coexisted, the TCE sorption capacity decreased significantly on BC-CK + PE, BC-HCl + PE, BC-HNO3 + PE, BC-NaOH + PE, and BC-NaOH + PS, which was likely due to the preferential sorption of PE/PS on BC samples. We concluded that microplastics can change TCE sorption behavior and inhibit TCE sorption on BC samples. Thus, the interaction of BC and microplastics should be considered when BC is used for TCE removal in soil and water remediation.

Alleviation of ZnO nanoparticles-induced methanogenic inhibition by granular activated carbon

A great deal of attention has been paid to the toxicology of ZnO nanoparticles (NPs) to wastewater anaerobic digestion, but few studies have assessed how to reduce their toxic effects. In this study, different dosages of granular activated carbon (GAC) were added into ZnO NPs-bearing wastewater anaerobic digestion system. It was found that although the extracellular polymeric substances resistance, which had been impaired by ZnO NPs, could not be recovered by GAC, the suppressed methane yield was greatly enhanced by promoting the conversions of butyrate and acetate into methane. GAC of 10, 20 and 30 g/L enhanced the methane yield to 69%, 79% and 97% from 42% of the control inhibited by 100 mg/L ZnO NPs. This was mainly because the adsorption of GAC could weaken the effective contact between ZnO NPs and microbes, and also adsorb some released Zn2+ that has contributed primarily to ZnO NPs toxicology. The reduced toxicity of ZnO NPs was attributed to the enrichment of the tolerant hydrogenotrophic methanogens and the direct interspecies electron transfer-linking partners of Methanosarcina with Geobacter/Syntrophomonas. These syntrophic partners potentially used GAC as a conduit to transfer electrons for methane production.

The Modification of Activated Carbon for the Performance Enhancement of a Natural-Rubber-Based Triboelectric Nanogenerator

Increasing energy demands and growing environmental concerns regarding the consumption of fossil fuels are important motivations for the development of clean and sustainable energy sources. A triboelectric nanogenerator (TENG) is a promising energy technology that harnesses mechanical energy from the ambient environment by converting it into electrical energy. In this work, the enhancement of the energy conversion performance of a natural rubber (NR)-based TENG has been proposed by using modified activated carbon (AC). The effect of surface modification techniques, including acid treatments and plasma treatment for AC material on TENG performance, are investigated. The TENG fabricated from the NR incorporated with the modified AC using N2 plasma showed superior electrical output performance, which was attributed to the modification by N2 plasma introducing changes in the surface chemistry of AC, leading to the improved dielectric property of the NR-AC composite, which contributes to the enhanced triboelectric charge density. The highest power density of 2.65 mW/m2 was obtained from the NR-AC (N2 plasma-treated) TENG. This research provides a key insight into the modification of AC for the development of TENG with high energy conversion performance that could be useful for other future applications such as PM2.5 removal or CO2 capture.

Recent progress in high-performance environmental impacts of the removal of radionuclides from wastewater based on metal-organic frameworks: a review

The nuclear industry is rapidly developing and the effective management of nuclear waste and monitoring the nuclear fuel cycle are crucial. The presence of various radionuclides such as uranium (U), europium (Eu), technetium (Tc), iodine (I), thorium (Th), cesium (Cs), and strontium (Sr) in the environment is a major concern, and the development of materials with high adsorption capacity and selectivity is essential for their effective removal. Metal-organic frameworks (MOFs) have recently emerged as promising materials for removing radioactive elements from water resources due to their unique properties such as tunable pore size, high surface area, and chemical structure. This review provides an extensive analysis of the potential of MOFs as adsorbents for purifying various radionuclides rather than using different techniques such as precipitation, filtration, ion exchange, electrolysis, solvent extraction, and flotation. This review discusses various MOF fabrication methods, focusing on minimizing environmental impacts when using organic solvents and solvent-free methods, and covers the mechanism of MOF adsorption towards radionuclides, including macroscopic and microscopic views. It also examines the effectiveness of MOFs in removing radionuclides from wastewater, their behavior on exposure to high radiation, and their renewability and reusability. We conclude by emphasizing the need for further research to optimize the performance of MOFs and expand their use in real-world applications. Overall, this review provides valuable insights into the potential of MOFs as efficient and durable materials for removing radioactive elements from water resources, addressing a critical issue in the nuclear industry.

Simple fabrication of carbon quantum dots and activated carbon from waste wolfberry stems for detection and adsorption of copper ion

Removal of heavy metal pollution is an endless topic, because heavy metals can cause irreversible damage to the human body and environment. It is urgent to develop novel materials for detection and adsorption of heavy metal ions. In this paper, waste wolfberry straw was utilized as a carbon source, and two simple methods were developed to successfully prepare activated carbon (AC) and carbon quantum dots (CQDs). The fabrication conditions were optimized by adjusting the mass ratio of precursor to activator, type of activator and activation times. When sodium hydroxide (NaOH) was selected as an activator (6 : 1, mass ratio of NaOH to AC-precursor), and the activation was performed at 600 °C for 1 h, the highest specific surface area of the obtained AC-NaOH-3 reached 3016 m² g^-1. The adsorption capacity for copper ions (Cu²⁺) reached 68.06 mg g^-1. The preparation conditions for CQDs were also optimized by adjusting the concentration of wolfberry stem, reaction time and temperature. When the wolfberry stem concentration was 7.5 g L^-1, and the activation was performed at 200 °C for 24 h, the obtained CQDs exhibited strong fluorescence emission in the blank and 12 kinds of metal ion solutions, respectively, however, the fluorescence intensity was remarkably decreased after adding Cu²⁺. In the range of 10-80 nM, the linear correlation coefficient between the concentration of Cu²⁺ and fluorescence intensity of CQDs was 0.992, and the limit of detection was 2.83 nmol L^-1. Thus, these two kinds of materials were prepared from wolfberry stem, which opened up a new way for the application in adsorption and detection of copper ions.

Modified Activated Carbon: A Supporting Material for Improving Clostridium beijerinckii TISTR1461 Immobilized Fermentation

This study aimed to investigate the effect of activated carbon (AC) as an immobilization material in acetone-butanol-ethanol fermentation. The AC surface was modified with different physical (orbital shaking and refluxing) and chemical (nitric acid, sodium hydroxide and, (3-aminopropyl)triethoxysilane (APTES)) treatments to enhance the biobutanol production by Clostridium beijerinckii TISTR1461. The effect of surface modification on AC was evaluated using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, surface area analyses, and X-ray photoelectron spectroscopy, while the fermented broth was examined by high-performance liquid chromatography. The chemical functionalization significantly modified the physicochemical properties of the different treated ACs and further enhanced the butanol production. The AC treated with APTES under refluxing provided the best fermentation results at 10.93 g/L of butanol, 0.23 g/g of yield, and 0.15 g/L/h of productivity, which were 1.8-, 1.5-, and 3.0-fold higher, respectively, than that in the free-cell fermentation. The obtained dried cell biomass also revealed that the treatment improved the AC surface for cell immobilization. This study demonstrated and emphasized the importance of surface properties to cell immobilization.

Enhanced adsorption capacity of activated carbon over thermal oxidation treatment for methylene blue removal: kinetics, equilibrium, thermodynamic, and reusability studies

Activated carbon (AC) is an effective and inexpensive adsorbent material for dye removal, but it cannot always be used repeatedly. Furthermore, the adsorbed dyes with toxicity usually remain on its surface. In this study, a thermal air oxidation process was used to modify the surface of AC and decompose adsorbed methylene blue (MB). The behavior of this process on spent AC was investigated using TGA-DTA, while the degradation of MB before and after the regeneration process was analyzed using a carbon, hydrogen, nitrogen, sulfur (CHNS) analyzer. It was discovered that thermal air oxidation could promote the formation of oxygenated functional groups on AC produced from steam-activated carbon coconut shell (SACCS), which when treated at 350 °C (denoted as SACCS-350), demonstrated an adsorption capacity 2.8 times higher than the non-air-oxidized AC (SACCS). The key parameters for the MB adsorption of SACCS and SACCS-350, such as kinetics, equilibrium, and thermodynamics, were compared. Moreover, the SACCS-350 could be reused at least 3 times for the adsorption of MB. Based on these results, thermal air oxidation treatment could successfully improve the adsorption performance of AC and regenerate spent AC through a reasonable and environmentally friendly process compared to other regeneration methods.

FTIR-Assisted Electroreduction of CO2 and H2O to CO and H2 by Electrochemically Deposited Copper on Oxidized Graphite Felt

Obtaining CO and H₂ from electrochemical CO₂ reduction (CO₂RR) offers a viable alternative to reduce CO₂ emissions and produce chemicals and fuels. Herein, we report a simple strategy for obtaining polycrystalline copper deposited on oxidized graphite felt (Cu-OGF) and its performance on the selective conversion of CO₂ and H₂O to CO and H₂. For the electrode obtaining, graphite felt (GF) was first oxidized (OGF) in order to make the substrate hydrophilic and then copper particles were electrochemically deposited onto OGF. The pH of deposition was investigated, and the CO₂RR activity was assessed for the prepared electrodes at each pH (2.0, 4.0, 6.0, 8.0, and 10.0). It was found that pH 2.0 was the most promising for CO₂RR due to the presence of hexagonal copper microparticles. Fourier transform infrared analysis of the produced gases showed that this is a low-cost catalyst capable of reducing CO₂ and H₂O to CO and H₂, with Faradaic efficiencies between 0.50 and 5.21% for CO and 50.87 to 98.30% for H₂, depending on the experimental conditions. Hence, it is possible for this gas mixture to be used as a fuel gas or to be enriched with CO for use in Fischer-Tropsch processes.

Removal of benzene, MTBE and toluene from contaminated waters using biochar-based liquid activated carbon

Fuel components such as benzene, toluene, and methyl tertiary-butyl ether (MTBE) are frequently detected pollutants in groundwater resources. Ex-situ remediation technologies by activated carbon have been used for treatment for many years. However, due to high cost of these technology, more attention has been given to the in-situ remediation methods of contaminated groundwaters using liquid carbon adsorbents. Literature search showed limited studies on using adsorbents in liquid form for the removal of such contaminants. Therefore, this lab-scale study investigates the capacity of using raw biochar-based liquid activated carbon and iron-modified biochar-based liquid activated carbon to remove these pollutants. The adsorption efficiency of the synthesized liquid activated carbon and iron-modified liquid activated carbon mixed with sand, limestone, and 1:1 mixture of sand/limestone, was tested using batch suspension experiments. Adsorption by granular activated carbon was also investigated for comparison with liquid activated carbon. Results of the study revealed that mixing of liquid activated carbon or LAC-Fe on subsurface materials had not improved the removal efficiency of MTBE. At the same time, it showed a slight improvement in the adsorption efficiency of benzene and toluene. In all cases, the removal by GAC was higher with around 80% and 90% for MTBE and BT, respectively. Results also showed that benzene and toluene were better removed by liquid activated carbon and iron-modified liquid activated carbon (∼ 40%) than MTBE (∼ 20%). It is also found that water chemistry (i.e., salinity and pH) had insignificant effects on the removal efficiency of pollutants under the study conditions. It can be concluded that more research is needed to improve the capacity of biochar-based liquid-activated carbon in removing MTBE, benzene and toluene compounds that will lead to improve the utilization of liquid activated carbon for the in-situ remediation of contaminated groundwaters.

Simulation Study of Electric Double-Layer Capacitance of Ordered Carbon Electrodes

Supercapacitors are electrochemical energy storage devices having high capacitance, high power density, long cycle life, low cost, easy maintenance, and negligible environmental pollution. The formation of an electric double layer at the electrode-electrolyte interface is mostly responsible for supercapacitors' energy storage. The simulation study of equilibrium electric double-layer capacitance (EDLC) in 3D arranged mesoporous carbon electrodes with a simple cubic morphology and interdigitated electrodes has been done. Continuum theory has been utilized to study the underlying processes involved in EDLC. Interfacial polarization and ion crowding depend on the electrode's critical thickness. Porosity increases the capacitance due to the increase in the electrode surface area. The diffuse-layer specific capacitance of ordered mesoporous carbon electrodes in a (C₂H₅)₄NBF₄/propylene carbonate organic electrolyte is in the range of 3.2-13.3 μF cm^-2, varying according to the electrode thickness. The Stern-layer specific capacitance is 167.6 μF cm^-2, and total equilibrium EDLC is in the range of 3.1-12.3 μF cm^-2. The effect of the electric field at the electrode-electrolyte interface on reducing electrolyte permittivity has also been discussed. The EDLC of carbonized interdigitated electrodes is analyzed in a 6 M KOH electrolyte. The diffuse-layer specific capacitance ranges from 118.7 to 352.0 μF cm^-2 depending on the width of the interdigitated electrodes. The Stern-layer specific capacitance is 91.2 μF cm^-2, and the total EDLC value is 51.6-72.4 μF cm^-2. The modeling and simulation approach can be applied to different mesoporous electrodes by varying the supercapacitor component's parameters and geometry.

Synthesis of Activated Carbon from Trachycarpus fortunei Seeds for the Removal of Cationic and Anionic Dyes

The removal of dyes from industrial effluents is one of the most important industrial processes that is currently on academic demand. In this project, for the first time, Trachycarpus fortunei seeds are used as biosources for the synthesis of activated carbon (AC) using physical as well as acid–base chemical methods. The synthesized AC was initially characterized by different instrumental techniques, such as FTIR, BET isotherm, SEM, EDX and XRD. Then, the prepared activated carbon was used as an economical adsorbent for the removal of xylenol orange and thymol blue from an aqueous solution. Furthermore, the effect of different parameters, i.e., concentration of dye, contact time, pH, adsorbent amount, temperature, adsorbent size and agitation speed, were investigated in batch experiments at room temperature. The analysis of different techniques concluded that the pyrolysis method created a significant change in the chemical composition of the prepared AC and the acid-treated AC offered a high carbon/oxygen composite, which is graphitic in nature. The removal of both dyes (xylenol orange and thymol blue) was increased with the increase in the dye’s initial concentration. Isothermal data suggested that the adsorption of both dyes follows the Langmuir model compared to the Freundlich model. The equilibrium time for AC biomass to achieve the removal of xylenol orange and thymol blue dyes was determined to be 60 min, and the kinetic data suggested that the adsorption of both dyes obeyed the pseudo-second order model. The optimal pH for thymol blue adsorption was pH 6, while it was pH 2 for xylenol orange. The adsorption of both dyes increased with the increase in the temperature. The influence of the adsorbent amount indicated that the adsorption capacity (mg/g) of both dyes reduced with the rise in the adsorbent amount. Thus, the current study suggests that AC prepared by an acid treatment from Trachycarpus fortunei seeds is a good, alternative, cost effective, and eco-friendly adsorbent for the effective removal of dyes from polluted water.

A nickel hydroxide platform prepared on a hydroxyl-enriched screen-printed carbon electrode for oxidative electrocatalysis

We report here the preparation of an activation-free Ni electrode (i.e., eventually the formation of NiOOH) through enrichment of hydroxyl functional groups via a base-catalyzed hydrolysis reaction on a "preanodized" screen printed carbon electrode. The as-prepared Ni electrode exhibits good electroanalytic performance for the flow injection analysis of glucose.

The effects of H2O2- and HNO3/H2SO4-modified biochars on the resistance of acid paddy soil to acidification

Biochar was prepared from rice straw and modified with 15% H₂O₂ and 1:1 HNO₃/H₂SO₄, respectively. The unmodified biochars and HCl treated biochars for carbonate removal were used as control. The biochars were added to the acid paddy soil collected from Langxi, Anhui Province, China at the rate of 30 g/kg. The paddy soil was flooded and then air-dried, and soil pH and Eh were measured in situ with pH electrode and platinum electrode during wet-dry alternation. Soil pH buffering capacity (pHBC) was determined by acid-base titration after the wet-dry treatment. Then, the simulated acidification experiments were carried out to study the changing trends of soil pH, base cations and exchangeable acidity. The results showed that soil pHBC was effectively increased and the resistance of the paddy soil to acidification was apparently enhanced with the incorporation of H₂O₂- and HNO₃/H₂SO₄-modified biochars. Surface functional groups on biochars were mainly responsible for enhanced soil resistance to acidification. During soil acidification, the protonation of organic anions generated by dissociation of these functional groups effectively retarded the decline of soil pH. The modification of HNO₃/H₂SO₄ led to greater increase in carboxyl functional groups on the biochars than H₂O₂ modification and thus HNO₃/H₂SO₄-modified biochars showed more enhancement in soil resistance to acidification than H₂O₂-modified biochars. After a wet-dry cycle, the pH of the paddy soil incorporated with HNO₃/H₂SO₄-modified biochar increased apparently. Consequently, the addition of HNO₃/H₂SO₄-modified biochar can be regarded as a new method to alleviate soil acidification. In short, the meaning of this paper is to provide a new method for the amelioration of acid paddy soils.

Physicochemical Properties of Membrane Adsorber from Palm Empty Fruit Bunch (PEFB) by Acid Activation

A membrane adsorbent was successfully made from palm empty fruit bunches (PEFB), which was pyrolysed as physical activation. The effect of adding the impact of one-step catalyst (hydrochloric acid) and differences in the concentration on the characteristics and structure and deconvolution are investigated in this study. The results of the research have been successfully created and characterised using Fourier-Transform Infrared (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) isotherm, and membrane morphology using SEM test. Membrane performance testing was carried out using a biogas flame test. The adsorber membrane was made by adding NH₄Cl as a cationic surfactant, polyvinyl acetate (PVA), and polyethylene glycol (PEG) with a ratio of 1:3. The FTIR test has a functional group: O-H; C-H stretch; C=C-C; Arly O-Strech; C-O. Adsorbent membrane with the addition of 0.5 M HCl catalyst had the highest ratio of O-H/C=C-C relative area of 4.33. The diffractogram shows an amorphous structure with (002) and (100) graph planes. Adsorber membrane with a concentration of 1.5 M HCl has formed amorphous structured fibre. The adsorber membrane with a concentration of 0.5 HCl activator gave a surface area of 0.5345 m² g⁻¹ and a pore volume of 0.000983 cm³ g⁻¹.

Enhancement of Cd(II) adsorption by rice straw biochar through oxidant and acid modifications

To develop high-efficient biochar adsorbents, the effects and mechanisms of oxidant modification and acid modification on Cd(II) adsorption by rice straw biochar were investigated. Three rice straws from Langxi in Anhui Province, Yingtan in Jiangxi Province, and Lianyungang in Jiangsu Province were collected to prepare biochars by anaerobic pyrolysis in a muffle furnace. Rice straw biochars were modified by 15% H₂O₂ and 1:1 HNO₃/H₂SO₄ mixed acid, respectively, to obtain modified biochars. The untreated rice straw biochar and HCl-treated rice straw biochar with carbonate removed were used as controls. The functional groups on the surfaces of the biochars were qualitatively and quantitatively determined by Fourier transform infrared spectra and Boehm titration, respectively. The adsorption and desorption of Cd(II) onto and from the biochars and modified biochars were measured under various pH conditions. The results showed that oxidant modification with 15% H₂O₂ and acid modification with 1:1 HNO₃/H₂SO₄ significantly increased the number of carboxyl functional groups on the surfaces of the biochars, and acid modification was more effective than oxidant modification in amplifying carboxyl functional groups on the surfaces of the biochars. The increase of surface functional groups effectively enhanced the specific adsorption of Cd(II) on the modified biochars. Therefore, both oxidant modification and acid modification enhanced the adsorption of Cd(II) on the biochars through increasing functional groups on the surfaces of the biochars.

Incorporating the recovered carbon black produced in an industrial-scale waste tire pyrolysis plant into a natural rubber formulation

This paper presents the experimental results obtained after incorporating the recovered Carbon Black (rCB) produced in an industrial-scale waste tire pyrolysis plant into a Natural Rubber (NR) formulation. The purpose of this study is to increase the technical knowledge on the use of rCB as a sustainable raw material in the rubber industry. The rCB and virgin Carbon Black (vCB) (ref. N550) under study were characterized using elemental and proximate analyses, X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM) were used, and different measures, including the Brunauer-Emmett-Teller (BET) surface area (S_BET), particle size distribution (PSD), specific gravity, and pH, were estimated. The effect of rCB incorporation on the rheological, thermal, structural, and mechanical properties of the NR composites was assessed and compared to those obtained with vCB alone. The NR composites were prepared using different loads of vCB (20, 30, 40, and 50 phr), which was also replaced with rCB at different proportions (0, 50, and 100%). According to the characterization results, rCB offers lower reinforcement properties than vCB, which is attributable to its higher volatile matter and ash contents, higher apparent PSD, lower presence of acidic functional groups, and lower S_BET. Despite this, interesting performances can be achieved when rCB is partially incorporated into the formulations or by increasing its load in the composites. For instance, when 50% of vCB was replaced with rCB, the values of the aforementioned properties were found to be between those obtained with the NR composites prepared with vCB and rCB. In addition, when increasing the rCB loading, some properties matched the behavior exhibited by vCB alone, thus compensating for the low reinforcement properties of rCB. These results are expected to provide an important impetus to move towards circular economy strategies having very positive impacts from the sustainable perspective.

Functionalization of ultrasound enhanced sewage sludge-derived biochar: Physicochemical improvement and its effects on soil enzyme activities and heavy metals availability

Poor physicochemical characteristics and high heavy metals content are main limitations of applying sludge-based biochars in remediation studies. The present study attempts to combine two practical approaches of ultrasound pre-treatment with low-time and low-frequency and chemical functionalization using citric acid. The aims of this study are enhancement physicochemical characteristics and environmental applicability of sludge-derived biochar. The characteristics of obtained ultrasound-treated functionalized biochar (UFB), sludge-derived biochar (SDB) and sewage sludge (SS) were evaluated. Then, the effects of these additives on soil heavy metals availability, soil enzyme activities and soil physicochemical characteristics were investigated during a 2-month stabilization process. The results indicated that ultrasound pre-treatment and functionalization considerably increased pore volume, surface area, and surface functional groups of the biochar, but significantly decreased total heavy metals concentration and metals ecological risk index (Er). The results of soil amending showed that application of UFB decreased Pb, Zn and Cd availability in soil by 85.3, 82.9 and 30.6%, respectively. In all cases, except for Cd, the Pb and Zn availability decreased by UFB was two times greater than the availability decreased by SDB and SS. Compared to SDB, the UFB potentially enhanced the positive effect of additive on soil enzyme activities. The obtained results revealed that the feasible, uncomplicated physical and chemical techniques can be used as a valuable approach for enhancing the environmental applicability of sludge-derived biochar and management of the excessively produced sewage sludge in the world.

A strategy for the enhancement of trapping efficiency of gaseous benzene on activated carbon (AC) through modification of their surface functionalities

Facile modification is a common, but effective, option to improve the uptake removal capacity of of activated carbon (AC) against diverse target volatile organic compounds (VOCs; e.g., benzene) in gaseous streams. To help design the routes for such modification, this research built strategies to generate three types of modified ACs by incorporating amine/sulfur/amino-silane groups under solvothermal or microwave (MW) thermal conditions. The adsorption performance has been tested using a total of six types of AC sorbents (three modified + three pristine forms) for the capture of 1 Pa benzene (1 atm and 298 K). The obtained results are evaluated in relation to their textural properties and surface functionalities. Accordingly, the enhancement of AC surface basicity (e.g., point of zero charge (PZC) = 10.25), attained via the silylation process, is accompanied by the reduced adsorption of benzene (a weak base). In contrast, ACs amended with amine/sulfur (electron-donating) groups using the MW technique are found to acquire high surface acidity (PZC of 5.99-6.05) to exhibit significantly improved benzene capturing capability (relative to all others). Their uplifted performance is demonstrated in terms of key performance metrics such as breakthrough volume (BTV10%: 163 → 443 L g^-1), adsorption capacity (Q10%: 4.82 → 13.6 mg g^-1), and partition coefficient (PC10%: 0.516 → 1.67 mol kg^-1 Pa^-1). Based on the kinetic analysis, the overall adsorption process is found to be governed by pore diffusion as the main rate-determining step, along with surface interaction mechanisms. The results of this research clearly support the critical role of surface chemistry of AC adsorbents and their textural properties in upgrading air/gas purification systems.

Activated carbon column adsorption of compounds that mimic urban stormwater dissolved organic nitrogen

Nutrients mobilized by stormwater can exacerbate eutrophication in receiving waters. While bioretention systems are increasingly employed to improve stormwater quality, they do not normally incorporate design attributes for removal of dissolved organic nitrogen (DON). Thus, the current study concentrated on continuous column adsorption of stormwater DON using a media mixture of coal activated carbon and quartz sand. Adsorption of eight model organic nitrogenous compounds was studied and only pyrrole showed an appreciable adsorption performance; other organic nitrogen compounds were weakly adsorbed. The breakthrough depth for pyrrole was 88 m (equivalent to 4.4 m simulated rainfall depth), at a superficial velocity of 61 cm/hr and influent DON concentration of 1 mg N/L. Subsequent experiments revealed that adsorption of pyrrole was minimally affected by superficial velocity, such that its DON removal efficiency was greater than 91% for all tested superficial velocities (7-489 cm/hr). Accordingly, adsorption processes may be employed for removing stormwater DON fractions behaving similarly to pyrrole; data suggest DON removal initially at greater than 95%, gradually falling to 30% through 25 years of service. PRACTITIONER POINTS: Adsorption of eight different organic nitrogenous compounds onto coal-based activated carbon was investigated. Amino acids and an amino sugar were weakly adsorbed onto the activated carbon. Pyrrole, a moderately hydrophobic heterocyclic organic nitrogen compound was effectively adsorbed. A 30-cm depth was considered as adequate for removal of pyrrole and compounds that would similarly adsorb. Evidence of biological ammonification was present in all studies except for pyrrole.

BET, FTIR, and RAMAN characterizations of activated carbon from waste oil fly ash

Activated carbon (AC), a porous material with high pore volume, attracts increasing attention owing to its potential applications in several fields. The development of a porous structure in AC marginally relies on both the treatment methods and the type of precursor. Thus far, both renewable and nonrenewable precursor sources have been used to synthesize AC with high surface area and pore volume. This study presents the synthesis of AC via physicochemical treatment of waste oil fly ash (OFA), a waste material produced from power plants. The aim was to produce AC by adding surface pores and surface functional groups to the basal plane of OFA. Toward this objective, OFA was first chemically leached/activated with various combinations of H₂SO₄ and H₃PO₄, and then physically activated with CO₂ at 900 °C. The chemical activation step, synergistically combined with CO₂ activation, resulted in an increase of 24 times the specific surface area of the OFA. The maximum increase in surface area was obtained for the sample physicochemically treated with 100% H₂SO₄ . Moreover, the spectroscopic analysis confirmed the presence of acid functional groups after the chemical treatment step. To explore the surface heterogeneity, adsorptive potential distribution in terms of surface energy was also discussed as a function of the surface coverage. Following chemical activation, the OFA surface became heterogeneous. A major portion of the AC showed surface energy in the range of 40–50 erg/K, which was further increased as a result of physical activation at a higher temperature. Thus, the synergism created by physicochemical activation resulted in a material with high surface area and pore volume, and excellent adsorption characteristics. From the findings of this study, it was concluded that OFA is a cost-effective and environmentally benign precursor for the synthesis of AC.

The Influence of Carbon Nature on the Catalytic Performance of Ru/C in Levulinic Acid Hydrogenation with Internal Hydrogen Source

The influence of the nature of carbon materials used as a support for Ru/C catalysts on levulinic acid hydrogenation with formic acid as a hydrogen source toward gamma-valerolactone was investigated. It has been shown that the physicochemical properties of carbon strongly affect the catalytic activity of Ru catalysts. The relationship between the hydrogen mobility, strength of hydrogen adsorption, and catalytic performance was established. The catalyst possessing the highest number of defects, stimulating metal support interaction, exhibited the highest activity. The effect of the catalyst grain size was also studied. It was shown that the decrease in the grain size resulted in the formation of smaller Ru crystallites on the catalyst surface, which facilitates the activity.

A WO3/PPy/ACF modified electrode in electrochemical system for simultaneous removal of heavy metal ion Cu2+ and organic acid

Heavy metal ions and organic acids are common pollutants in electroplating wastewater. Effective and economic treatment of such wastewater needs novel technologies. In this study, WO₃/PPy-1/ACF electrode was prepared using a hydrothermal modification method and it has large specific area (788.27 m² g^-1), high areal capacitance (2.58 F cm^-2 under 5 mA cm^-2 charge and discharge) and excellent conductivity. The modified electrode was used in an electrochemical system with activated carbon fiber felt (ACF) as counter electrode. The system simultaneously and successfully removed 97.8 % Cu²⁺ and 80.1 % citric acid (CA) from a simulated electroplating wastewater (typically 100 mg L^-1 Cu²⁺ and 800 mg L^-1 CA) in five- hour optimized operation. The influence of operating parameters (circulating inflow rate, applied voltage and influent pH) on the treatment performance was compared. There is interplay between Cu²⁺ reductive deposition and CA oxidation. The synergetic electrochemical treatment mechanism involves formation of hydrogen peroxide, free radicals, and catalytic effect of Cu species was proposed. This electrochemical system which is low-cost, easy to operate and highly efficient, may be applicable in treating acid-wash or electroplating wastewater, containing heavy-metal ions and organic acids.

Assessment of Cd(II) adsorption capability and mechanism from aqueous phase using virgin and calcined lignin

Herein, to assess the adsorption capability and elucidate the adsorption mechanism of Cd(II) from the aqueous phase, virgin lignin (Lig) and calcined lignin (Lig200, Lig400, Lig600, Lig800, and Lig1000) were prepared. The characteristics, including specific surface area and pore volume of adsorbents, were investigated, and the adsorption capability along with the effect of temperature, contact time, and pH on the adsorption of Cd(II) were evaluated. The characteristics of the adsorbent surface were related to the adsorption capability of Cd(II) from the aqueous phase, and the correlation coefficients between the adsorbed amount and specific surface area and total pore volumes were 0.872 and 0.960, respectively. Moreover, the amount adsorbed using Lig800 (91.3 mg/g) was higher than that using other adsorbent samples. The adsorption mechanism was elucidated to investigate the binding energy and elemental distribution before and after Cd(II) adsorption. Finally, the desorption capability of Cd(II) from Lig800 using a hydrochloric acid solution was demonstrated. Results obtained herein suggest that Lig800 is a potential candidate for the removal of Cd(II).

Gasification biochar from biowaste (food waste and wood waste) for effective CO2 adsorption

Biochar is newly proposed as an innovative and cost-effective material to capture CO₂. In this study, biochar was produced from feedstock mixtures of food waste and wood waste (i.e., 20%:80% WFW20, 30%:70% WFW30 and 40%:60% WFW40) by gasification. The two biochar adsorbents containing the highest percentage of food waste, i.e., WFW40-K and WFW40-KC, were activated by KOH and KOH + CO₂, respectively. The biochar adsorbents were then tested for CO₂ adsorption at room temperature of 25 °C by using a volumetric sorption analyzer. The WFW20 showed the highest CO₂ adsorption capacity, while higher percentage of food waste in the feedstock was unfavorable for the CO₂ adsorption. The presence of N and S on the biochar surface was the primary contributor to the high CO₂ uptake on WFW20. The development of micropores by KOH activation significantly increased the CO₂ adsorption on WFW40-K, but KOH + CO₂ activation could not further increase the development of micropores and subsequent CO₂ adsorption. Moreover, WFW40-K showed >99% recyclability during 10 consecutive adsorption-desorption cycles. The biochars derived from biowaste (food waste and wood waste) could be effective adsorbents for CO₂ capture by providing green solution for food waste recycling.

The interaction of metallic ions onto activated carbon surface using computational chemistry software

Activated carbon was prepared from the seeds of aguaje palm ( Mauritia flexuosa L.f.) by a chemical activation with phosphoric acid. This activated carbon was used for adsorbing metal ions: Pb(II), Cd(II), and Cr(III). To understand the mechanism of adsorption of these heavy metals (Cr, Cd, and Pb), the activated carbon surface was oxidized with nitric acid (1 M) increasing the oxygenated surface groups showing an increasing in their adsorption capacities of these metals. The oxidized activated carbon slightly increased the maximum adsorption capacity to 5–7%. The order of adsorption for unoxidized and oxidized activated carbons was Pb> Cd> Cr. This experimental information was corroborated by molecular modeling program Hyperchem 8 based adsorption mainly on two factors: the electron density and orbitals—highest occupied molecular orbital and lowest unoccupied molecular orbital.Activated carbons were characterized by adsorption/desorption of N2, obtaining an increase of microporous surface area for oxidized activated carbon. An increase of surface acidity and a reduction of isoelectric points were observed in oxidized activated carbon. According to these results, the adsorption of metal ions is favored in contact with an oxidized activated carbon, which has more amount of phenolic and carboxylic functional groups. Similarly, decreasing the isoelectric point indicates that the surface has a higher negative charge. The surface information was corroborated by Hyperchem, which indicates that the surface of the oxidized activated carbon has a higher electron density, indicating a larger amount of electrons on its surface, which means the surface of oxidized activated carbon charges negatively and thereby attracts metal ions.

Microwave-Assisted Preparation of Activated Carbon Modified by Zinc Chloride as a Packing Material for Column Separation of Saccharides

Activated carbon, an amorphous carbon material with a high specific surface area and void fraction, is widely used as an economical adsorbent in many fields. In this work, a kind of new activated carbon composite for saccharide column separation was prepared by zinc chloride impregnating and microwave heating. The structural characterizations validate the increase in porosity and the specific surface area of the activated carbon as well as the change of the activated carbon crystallite lattice. The chemical characterizations validate the increase in the number of oxygen-containing functional groups and structural bonding of zinc with the activated carbon surface. Compared with the blank control, the surface Zn element improves the adsorption selectivity of the activated carbon to the target saccharides. Under the special mechanism of microwaves, the pores created by expansion from the inside to the outside facilitate the free flow of the mobile phase. The eight saccharides can be separated by the columns packed with the activated carbon impregnated with 40% and 70% zinc chloride.

The role of the oxygen functional groups in adsorption of copper (II) on carbon surface

The effect of carbon surface oxidation on the adsorption of Cu(II) ions from aqueous solution was studied in order to explain the role of the oxygen functional groups in the binding of copper ions. Pristine carbonaceous adsorbent was oxidized to a various extent of oxygen uptake (Fenton-like oxidation < persulphate in H₂SO₄ < H₂O₂ in HNO₃). Equilibrium adsorption tests were performed in acetate buffer at pH ≈ 5. The results show that the adsorption capacity of pristine adsorbent is expectable low (~0.1 mmol g^-1). The oxidized samples adsorb Cu(II) at a considerably higher level of ~1.4 mmol g^-1 despite the degree of surface oxidation. Analysis of the surface groups (FTIR, TPD) and surface charge (zeta potential) of used adsorbents and their Cu(II) saturated counterpart lead to the finding that Cu(II) ions are mostly bonded by complexation with the dissociated carboxylic groups (partly formed by anhydrides hydrolysis) probably in the form of Cu(Ac)⁺ formed in the acetate buffer. The extent of dissociation is given by equilibrium pH during the adsorption and does not depend on the total amount of the surface groups. Thus, the content of active sites and consequently adsorption capacity is independent on the degree of oxidation when pH is kept constant. The results indicate that even moderate oxidation treatment of carbonaceous materials can produce highly effective adsorbents for Cu(II) immobilization.

Current advancement and future prospect of biosorbents for bioremediation

The increasing use of heavy metals, synthetic dyes and pesticides is a major environmental concern. Wastewaters containing heavy metals and dyes, extensively released from small and large scale industries enter excessively into food chains resulting in mutagenesis, carcinogenicity and serious health impairments in living systems. The arrays of technologies are implemented to date to remediate both inorganic and organic contaminants from wastewaters. Among which, adsorption is the most attractive method as it employs eco-friendly, sustainable and cost-effective biomaterials. Use of bioadsorbents is advantageous over the conventional adsorbents. Clay, chitin, peat, microbial biomass and agricultural wastes are commonly used bioadsorbants. These bioadsorbents are extensively used for elimination of dyes, heavy metals, adsorption of toxic industrial effluents, removal of fertilizers/pesticides, atmospheric pollutants and nuclear waste from the environment. The current review presents state of the art knowledge on various types of biosorbents, their uses, and mechanism of action. Various strategies to enhance the efficiency of bioadsorbents and physicochemical conditions to remediate dyes and heavy metals from waste streams are also incorporated in this review. Use of nano-bioadsorbents in industries to minimize the hazardous effect of solid and liquid waste has also been discussed.

Polyethyleneimine-modified biochar for enhanced phosphate adsorption

Biochar, a low-cost porous carbonaceous adsorbent, has low adsorption capacity for anion contaminants. The objective of this study was to improve biochar's ability to adsorb phosphorus (P) through polyethyleneimine (PEI) modification to form an amine-functionalized biochar. Biochars prepared by pyrolysis of bamboo biomass, before and after PEI modification, were characterized using the Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), elemental analysis, and batch sorption experiments. The effects of pH, coexisting anions, and ionic strength on P adsorption by PEI-modified biochar were also investigated. Results indicated that PEI was successfully grafted onto biochar which resulted an increase in surface amine group and in P adsorption. The peak of P adsorption occurred at pH of three and adsorption of P was decreased with increasing of ionic strength and when coexisting ions, such as HCO₃^-, SO₄^2-, NO₃^-, and Cl^-, were coexisted. The electrostatic interaction between P and surface functional groups of PEI-modified biochar served as the primary mechanism controlling the adsorption process. These results indicate that chemically functionalized biochar with amine groups can enhance P adsorption.

Intelligent-activated carbon prepared from pistachio shells precursor for effective adsorption of heavy metals from industrial waste of copper mine

A novel and efficient bio-adsorbent based on magnetic activated carbon nanocomposites (MAC NCs)-modified by sulfamic acid (H₃NSO₃) has been developed from pistachio shell precursor as agricultural by-products and then was applied for heavy metal removal. Design an experimental model (Central Composite Design (CCD)) for adopting surface response could efficiently be used for adsorption process, and it is an economical way of obtaining the optimal adsorption conditions based on the limited number of experiments. The variants of adsorbent dosage, metal ion concentration, and contact time were optimized for Cu(II) metal by CCD. In addition, adsorption capacity and isoelectric point (pHzpc) of adsorbent were studied at different pH values. Kinetic and isotherm of adsorption were investigated via the Langmuir and the pseudo-second-order model. The maximum adsorption capacity using the Langmuir model was 277.77 mg g^-1 for Cu(II) ions on H₂NSO₃-MAC NCs. Then adsorption process was investigated for ions of Fe(II), Zn(II), and Ni(II) under optimized condition. Also, the competitive adsorption of Fe(II), Zn(II), and Ni(II) ions mixed solution onto H₂NSO₃-MAC NCs was conducted. Adsorption-desorption results exhibited that the H₂NSO₃-MAC NCs can be used up to seven cycles while they have excellent performance. Finally, to evaluate the efficiency of this bio-adsorbent, the removal of heavy metals from wastewater of the Sarcheshmeh copper mine as a real sample was studied. Graphical abstract.

Selective adsorption of nitrate over chloride in microporous carbons

Activated carbon is the most common electrode material used in electrosorption processes such as water desalination with capacitive deionization (CDI). CDI is a cyclic process to remove ions from aqueous solutions by transferring charge from one electrode to another. When multiple salts are present in a solution, the removal of each ionic species can be different, resulting in selective ion separations. This ion selectivity is the result of combined effects, such as differences in the hydrated size and valence of the ions. In the present work, we study ion selectivity from salt mixtures with two different monovalent ions, chloride and nitrate. We run adsorption experiment in microporous carbons (i.e., without applying a voltage), as well as electrosorption experiments (i.e., based on applying a voltage between two carbon electrodes). Our results show that i) during adsorption and electrosorption, activated carbon removes much more nitrate than chloride; ii) at equilibrium, ion selectivity does not depend strongly on the composition of the water, but does depend on charging voltage in CDI; and iii) during electrosorption, ion selectivity is time-dependent. We modify the amphoteric Donnan model by including an additional affinity of nitrate to carbon. We find good agreement between our experimental results and the theory. Both show very high selectivity towards nitrate over chloride, [Formula: see text] ∼10, when no voltage is applied, or when the voltage is low. The selectivity gradually decreases with increasing charging voltage to [Formula: see text] ∼6 at V_ch = 1.2 V. Despite this decrease, the affinity-effect for nitrate continues to play an important role also at a high voltage. In general, we can conclude that our work provides new insights in the importance of carbon-ion interactions for electrochemical water desalination.

Comparison of the lead and copper adsorption capacities of plant source materials and their biochars

Lead (Pb) and Cu are the most common pollutants found in industrial effluents which affect ecosystem and human health. To remove Pb and Cu from aquatic system, cost-effective and environmentally friendly adsorbents are required. Therefore, the study evaluated the adsorption of Pb and Cu by waste plant materials and their biochars. The adsorption kinetics and isotherms were applied to compare the Pb and Cu adsorption capacities using the gingko (Spiraea blumei) leaf (GL), peanut shell (PS), and Metasequoia leaf (ML), and their derived biochars (GB, PB, and MB, respectively). The GB showed a significantly higher Pb adsorption capacity than the other adsorbents. Maximum Pb adsorption by GB was 138.9 mg/g followed by GL (117.6 mg/g). The highest Cu adsorption (59.9 mg/g) was also achieved by GB followed by GL (57.8 mg/g). The carbonates and the phosphate functional groups in the GB and higher affinity of Pb to the functional groups contributed to higher Pb adsorption. The Pb adsorption kinetics on the plant source materials and their biochars followed a pseudo-second order model. The Pb and Cu adsorption capacities, with the exception of the GL, ML, and GB, are better explained by Langmuir-isotherm models. The carbonization did not always lead to better heavy metal adsorption. The Pb and Cu adsorption significantly reduced with carbonization of ML because of disappearance of oxygen containing functional groups. Therefore, appropriate method to prepare metal adsorbent should be selected depending on feedstocks and metal removal mechanisms. The GL is the most-abundant fallen leaf in the streets of the Republic of Korea; therefore, the use of the GL biochar for heavy-metal adsorption will also reduce the cost for waste disposal.

Removal of chromium (VI) from aqueous solutions using Diospyros discolor seed activated with nitric acid: isotherm and kinetic studies

Diospyros discolor seed activated with nitric acid was investigated for removing Cr(VI) from aqueous solutions. Batch experiments were used to determine the adsorption efficiency, effect of pH, adsorption isotherm, and kinetics. Langmuir and Freundlich adsorption models were used to analyze data of Cr(VI) uptake. Fourier transform infrared spectroscopy was used to investigate the functional groups and surface morphology was checked using a scanning electron microscope, coupled with energy dispersive spectroscopy. The optimum pH in Cr(VI) uptake was 3.5 and the maximum adsorption efficiency reached 100% at 60 min.