Green conversion of crop residues into porous carbons and their application to efficiently remove polycyclic aromatic hydrocarbons from water: Sorption kinetics, isotherms and mechanism

Efficient selective adsorption of Cr(VI) by S-doped porous carbon prepared from industrial lignin: Waste increment and wastewater treatment

Industrial lignin is a waste product of the paper industry, which contains a large amount of oxygen group structure, and can be used to treat industrial wastewater containing Cr(VI). However, lignin has very low reactivity, so how to enhance its adsorption performance is a major challenge at present. In this study, a two-stage hydrothermal and activation strategy was used to activate the lignin activity and doping S element to prepare high-performance S-doped lignin-based polyporous carbon (S-LPC). The results show that the surface of S-LPC is rich in S and O groups and has a well-developed pore structure, which is very beneficial to Cr(VI) uptake -reduction and mass transfer on the material. In the wastewater, the utmost adsorption potential of Cr(VI) by S-LPC achieved 882.83 mg/g. After 7 cycles of regeneration, the adsorption of S-LPC decreased by only approximately 18 %. Ion competition experiments showed that S-LPC has excellent specificity for Cr(VI) adsorption. In factory wastewater, the adsorption performance of S-LPC for Cr(VI) remained above 95 %, which shows the excellent performance of S-LPC in practical applications. The results are of great significance for green chemical utilization of waste lignin, treatment of industrial wastewater and sustainable development.

Asparagus officinalis Herb-Derived Carbon Quantum Dots: Luminescent Probe for Medical Diagnostics

The utilization of natural materials for the synthesis of highly fluorescent carbon quantum dots (CQDs) presents a sustainable approach to overcome the challenges associated with traditional chemical precursors. Here, we report the synthesis of novel S,N-self-doped CQDs (S,N@CQDs) derived from asparagus officinalis herb. These S,N@CQDs exhibit 16.7 % fluorescence quantum yield, demonstrating their potential in medical diagnostics. We demonstrate the efficacy of S,N@CQDs as luminescent probes for the detection of anti-pathogenic medications metronidazole (MTZ) and nitazoxanide (NTZ) over concentration ranges of 0.0-180.0 μM (with a limit of detection (LOD) of 0.064 μM) and 0.25-40.0 μM (LOD of 0.05 μM), respectively. The probes were successfully applied to determine MTZ and NTZ in medicinal samples, real samples, and spiked human plasma, with excellent recovery rates ranging from 99.82 % to 103.03 %. Additionally, S,N@CQDs demonstrate exceptional efficacy as diagnostic luminescent probes for hemoglobin (Hb) detection over a concentration range of 0-900 nM, with a minimal detectability of 9.24 nM, comparable to commercially available medical laboratory diagnostic tests. The eco-friendly synthesis and precise detection limits of S,N@CQDs meet necessary analytical requirements and hold promise for advancing diagnostic capabilities in clinical settings. This research signifies a significant step towards sustainable and efficient fluorescence-based medical diagnostics.

Kinetics analysis of PAHs degradation using SiO2-ZnO nanoparticles and evaluating their antibacterial and antibiofilm efficacy

The adsorption of Polycyclic aromatic hydrocarbons (PAHs) using nanoparticles is gaining significant attention due to the rapid removal or treatment rates. In this study, Silicon Dioxide-Zinc Oxide nanoparticles (SiO2-ZnO NPs) were synthesized to adsorb pyrene. Physicochemical characterization of SiO2-ZnO NPs showed plasmon resonance at 323 nm, agglomeration, irregular dispersion, and diameters of 90-100 nm. FT-IR analysis identified major functional groups on SiO2-ZnO NPs, including alkyne, amine, and isothiocyanate. SiO2-ZnO NPs demonstrated significant pyrene adsorption at pH 5, with 10 μg/mL of SiO2-ZnO NPs and 2 μg/mL of PAHs, performing better under UV irradiation. Two isotherm models, adsorption isotherm and kinetics adsorption, were used to analyze the PAHs adsorption by SiO2-ZnO NPs. Additionally, SiO2-ZnO NPs were tested for antibacterial and antibiofilm activities against both Gram-negative and Gram-positive bacteria. At a concentration of 150 μg/mL, SiO2-ZnO NPs produced inhibition zones of 21.57 mm, 20.30 mm, 19.30 mm, and 11.30 mm against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Klebsiella pneumoniae, respectively. They also inhibited and disrupted biofilms of Micrococcus luteus and Acinetobacter baumannii. Furthermore, SiO2-ZnO NPs exhibited photocatalytic degradation of lead, achieving 68.24% degradation within 5 h of treatment. Therefore, SiO2-ZnO NPs are efficient candidates for multiple applications, including pyrene adsorption, bacterial biofilm disruption, and lead degradation under sunlight.

Effects of different precursors on the structure of lignin-based biochar and its ability to adsorb benzopyrene from sesame oil

Agricultural by-products of sesame are promising bioresources in food processing. This study extracted lignin from the by-products of sesame oil production, namely, the capsules and straw of black and white sesame. Using acid, alkali, and ethanol methods, 12 distinct lignins were obtained to prepare biochar, aiming to investigate both the structural characteristics of lignin-based biochar (LBB) and its ability to remove benzo[a]pyrene (BaP) from sesame oil. The results showed that white sesame straw was the most suitable raw material for preparing biochar. In terms of the preparation method, acid-extracted lignin biochar was more effective in removing BaP than alkaline or ethanol methods. Notably, WS-1LB (white sesame straw acid-extracted lignin biochar) exhibited the highest BaP adsorption efficiency (91.44 %) and the maximum specific surface area (1065.8187 m2/g), characterized by porous structures. The pseudo 2nd and Freundlich models were found to be the best fit for the adsorption kinetics and isotherms of BaP on LBB, respectively, suggesting that a multilayer adsorption process was dominant. The high adsorption of LBB mainly resulted from pore filling. This study provides an economical and highly efficient biochar adsorbent for the removal of BaP in oil.

A systematic review on enhancement strategies in biochar-based remediation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are pervasive ecological pollutants produced essentially during the inadequate burning of organic materials. PAHs are a group of different organic compounds that are made out of various aromatic rings. PAHs pose a serious risk to humans and aquatic ecosystems because of their mutagenic and carcinogenic properties. In this way, there is a critical prerequisite to utilizing successful remediation strategies and methods to limit the dangerous effect of these pollutants on the ecosystem. Biochar has believed of intriguing properties such as simple manufacturing operations and more affordable and more productive materials. Biochar is a sustainable carbonaceous material that has an enormous surface area with bountiful functional groups and pore structure, which has huge potential for the remediation of toxic pollutants. This review emphasizes the occurrence, development, and fate of toxic PAHs in the environment. In the present review, the properties and role of biochar in the removal of PAHs were illustrated, and the influencing factors and an efficient key mechanism of biochar for the remediation of PAHs were discussed in detail. Various surface modification methods can be utilized to improve the biochar properties with the magnetization process; the advancements of modified biochar are pointed out in this review. Finally, the constraints and prospects for the large-scale application of biochar in the remediation of toxic pollutants are highlighted.

Comparison of methods for activating sesame stalk lignin biochar for removing benzo[a]pyrene from sesame oil

In this study, three activators and two activation methods were employed to activate sesame lignin-based biochar. The biochar samples were comprehensively characterized, their abilities to adsorb benzo[a]pyrene (BaP) from sesame oil were assessed, and the mechanism was analyzed. The results showed that the biochar obtained by one-step activation was more effective in removing BaP from sesame oil than the biochar produced by two-step activation. Among them, the biochar generated by one-step activation with ZnCl2 as the activator had the largest specific surface area (1068.8776 m3/g), and the richest mesoporous structure (0.7891 m3/g); it removed 90.53 % of BaP from sesame oil. BaP was mainly adsorbed by the mesopores of biochar. Mechanistically, pore-filling, π-π conjugations, hydrogen bonding, and n-π interactions were involved. The adsorption was spontaneous and heat-absorbing. In conclusion, the preparation of sesame lignin biochar using one-step activation with ZnCl2 as the activator was found to be the best for removing BaP from sesame oil. This biochar may be an economical adsorbent for the industrial removal of BaP from sesame oil.

Nitrogen-Doped Biochar for Enhanced Peroxymonosulfate Activation to Degrade Phenol through Both Free Radical and Direct Oxidation Based on Electron Transfer Pathways

Nowadays, super nitrogen-doped biochar (SNBC) material has become one of the most promising metal-free catalysts for activating peroxymonosulfate (PMS) to degrade organic pollutants. To understand the evolution of SNBC properties with fabrication conditions, a variety of SNBC materials were prepared and characterized by elemental analysis, N2 adsorption-desorption, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. We systematically investigated the activation potential of these SNBC materials for PMS to degrade phenol. SN1BC-800 with the best catalytic performance was obtained by changing the activation temperatures and the ratio of biochar to melamine. The effects of catalyst dosage, the PMS concentration, pH, and reaction temperature on phenol degradation were studied in detail. In the presence of 0.3 g/L SN1BC-800 and 1 g/L PMS, the removal rate of 20 mg/L phenol could reach 100% within 5 min. According to electron paramagnetic resonance spectra and free radical quenching experiments, a nonfree radical pathway of phenol degradation dominated by 1O2 and electron transfer was proposed. More interestingly, the excellent catalytic performance of the SN1BC-800/PMS system is universally applicable in the degradation of other typical organic pollutants. In addition, the degradation rate of phenol is still over 80% after five reuses, which shows that the SN1BC-800 catalyst has high stability and good application prospects in environmental remediation.

Biochar-based materials as remediation strategy in petroleum hydrocarbon-contaminated soil and water: Performances, mechanisms, and environmental impact

Petroleum contamination is considered as a major risk to the health of humans and environment. Biochars as low-cost and eco-friendly carbon materials, have been widely used for the removal of petroleum hydrocarbon in the environment. The purpose of this paper is to review the performance, mechanisms, and potential environmental toxicity of biochar, modified biochar and its integration use with other materials in petroleum contaminated soil and water. Specifically, the use of biochar in oil-contaminated water and soil as well as the factors that could influence the removal ability of biochar were systematically evaluated. In addition, the modification and integrated use of biochar for improving the removal efficiency were summarized from the aspects of sorption, biodegradation, chemical degradation, and reusability. Moreover, the functional impacts and associated ecotoxicity of pristine and modified biochars in various environments were demonstrated. Finally, some shortcoming of current approaches, and future research needs were provided for the future direction and challenges of modified biochar research. Overall, this paper gain insight into biochar application in petroleum remediation from the perspectives of performance enhancement and environmental sustainability.

Carbon-based adsorbents for the mitigation of polycyclic aromatic hydrocarbon: a review of recent research

Accumulation of polycyclic aromatic hydrocarbons (PAH) poses significant dangers to the environment and human health. The advancement of technology for cleaning up PAH-contaminated environments is receiving more attention. Adsorption is the preferred and most favorable approach for cleaning up sediments polluted with PAH. Due to their affordability and environmental friendliness, carbonaceous adsorbents (CAs) have been regarded as promising for adsorbing PAH. However, adsorbent qualities, environmental features, and factors may all significantly impact how well CAs remove PAH. According to growing data, CAs, most of which come from laboratory tests, may be utilized to decontaminate PAH in aquatic setups. However, their full potential has not yet been established, especially concerning field applications. This review aims to concisely summarize recent developments in CA, PAH stabilization processes, and essential field application-controlling variables. This review analysis emphasizes activated carbon, biochar, Graphene, carbon nanotubes, and carbon-nanomaterials composite since these CAs are most often utilized as adsorbents for PAH in aquatic systems.

Critical review on the formations and exposure of polycyclic aromatic hydrocarbons (PAHs) in the conventional hydrocarbon-based fuels: Prevention and control strategies

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the atmosphere and primarily originate from the incomplete burning of fossil fuels and biofuels. Exposure to PAHs leads to harmful effects on human health and the environment. Diesel engines are a major source of PAH production in the transportation sector. Various approaches have been employed to reduce PAH emissions from diesel engines, including the use of biodiesel, green gaseous fuels, exhaust gas recirculation, exhaust after-treatment, and genetically modifying biodiesel with nanoparticles. This review focuses on PAH emissions from different generations of fuels and examines the remedial control actions taken to mitigate PAH formation. The study underscores the necessity for effective regulation of emissions from diesel engines, especially in developing countries where the reliance on fossil fuels is significant. Biodiesel has shown promise in reducing PAHs and carcinogenic pollutants, with higher biodiesel concentrations resulting in lower PAH formation. Replacing diesel with biodiesel and optimizing engine operating conditions are feasible methods to reduce PAH levels in the atmosphere. The use of nanoparticles in fuel blends and higher oxygen content in combustion chambers are also considered potential strategies for pollutant reduction. Additionally, the utilization of hydrogen and ammonia as secondary fuels has been explored as promising alternatives to fossil fuels. The study highlights the importance of further research on the presence of residual PAHs in the atmosphere and the implementation of strategies to curtail vehicular emissions.

Degradation of polycyclic aromatic hydrocarbons in aquatic environments by a symbiotic system consisting of algae and bacteria: green and sustainable technology

Polycyclic aromatic hydrocarbons (PAHs) are genotoxic, carcinogenic, and persistent in the environment and are therefore of great concern in the environmental protection field. Due to the inherent recalcitrance, persistence and nonreactivity of PAHs, they are difficult to remediate via traditional water treatment methods. In recent years, microbial remediation has been widely used as an economical and environmentally friendly degradation technology for the treatment of PAH-contaminated water. Various bacterial and microalgal strains are capable of potentially degrading or transforming PAHs through intrinsic metabolic pathways. However, their biodegradation potential is limited by the cytotoxic effects of petroleum hydrocarbons, unfavourable environmental conditions, and biometabolic limitations. To address this limitation, microbial communities, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively investigated. The advantages of algal-bacterial cocultivation have been explored, and the limitations of PAHs degradation by monocultures of algae or bacteria have been overcome by algal-bacterial interactions. Therefore, a new model consisting of a "microalgal-bacterial consortium" is becoming a new management strategy for the effective degradation and removal of PAHs. This review first describes PAH pollution control technologies (physical remediation, chemical remediation, bioremediation, etc.) and proposes an algal-bacterial symbiotic system for the degradation of PAHs by analysing the advantages, disadvantages, and PAH degradation performance in this system to fill existing research gaps. Additionally, an algal-bacterial system is systematically developed, and the effects of environmental conditions are explored to optimize the degradation process and improve its technical feasibility. The aim of this paper is to provide readers with an effective green and sustainable remediation technology for removing PAHs from aquatic environments.

Preparation of N-doped porous biochar with high specific surface area and its efficient adsorption for mercury ion from aqueous solution

Herein, a new type of super active nitrogen-doped biochar sheet (SNBC) was prepared by two-step pyrolysis and KOH chemical activation with melamine and cherry kernel powder as precursors of nitrogen and carbon source for removing Hg2+ from wastewater. The N2 adsorption/desorption and scanning electron microscope characterization revealed that the resulted SNBC under 600 °C calcination owned huge specific surface area of 2828 m2/g and plenty of well-developed micropores, and X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy analysis testified the existence of functional groups containing N and O, which could provide adsorption sites for Hg2+. The SNBC-600 showed high adsorption capacity for Hg2+ even at low pH, and interfering cations had little effect on the adsorption. The adsorption process was rapid and dynamic data fit the pseudo-second-order dynamic model well. The maximum adsorption capacity of Hg2+ on SNBC-600 calculated by Langmuir model was 230 mg/g. After six times of reuse, the adsorption capacity still exceeded 200 mg/g, exhibiting good reusability. The designed microfiltration membrane device base on SNBC-600 could remove low concentration of Hg2+ effectively from solution. This study provided a simple and environment-friendly method for manufacturing nitrogen-doped biochar sheet, which was of great significance in the practical application of Hg2+ pollution treatment.

Biomass waste-derived carbon materials for sustainable remediation of polluted environment: A comprehensive review

In response to the growing global concern over environmental pollution, the exploration of sustainable and eco-friendly materials derived from biomass waste has gained significant traction. This comprehensive review seeks to provide a holistic perspective on the utilization of biomass waste as a renewable carbon source, offering insights into the production of environmentally benign and cost-effective carbon-based materials. These materials, including biochar, carbon nanotubes, and graphene, have shown immense promise in the remediation of polluted soils, industrial wastewater, and contaminated groundwater. The review commences by elucidating the intricate processes involved in the synthesis and functionalization of biomass-derived carbon materials, emphasizing their scalability and economic viability. With their distinctive structural attributes, such as high surface areas, porous architectures, and tunable surface functionalities, these materials emerge as versatile tools in addressing environmental challenges. One of the central themes explored in this review is the pivotal role that carbon materials play in adsorption processes, which represent a green and sustainable technology for the removal of a diverse array of pollutants. These encompass noxious organic compounds, heavy metals, and organic matter, encompassing pollutants found in soils, groundwater, and industrial wastewater. The discussion extends to the underlying mechanisms governing adsorption, shedding light on the efficacy and selectivity of carbon-based materials in different environmental contexts. Furthermore, this review delves into multifaceted considerations, spanning the spectrum from biomass and biowaste resources to the properties and applications of carbon materials. This holistic approach aims to equip researchers and practitioners with a comprehensive understanding of the synergistic utilization of these materials, ultimately facilitating effective and affordable strategies for combatting industrial wastewater pollution, soil contamination, and groundwater impurities.

Effective Use of Sugarcane-Bagasse-Derived KOH-Activated Biochar for Remediating Norfloxacin-Contaminated Water

Bagasse-derived biochar (SCB750) was prepared at 750 °C using Chinese sugarcane bagasse as a carbon source and then modified with KOH for the removal of the antibiotic norfloxacin (NOR) from aqueous solutions. 3K-SCB750, prepared using a solid-to-liquid mass ratio of bagasse:KOH = 1:3, was found to have the best adsorption performance for NOR. Under the conditions of pH 5, 25 °C, 2.4 g L-1 adsorbent, and 300 mg L-1 NOR, its adsorption of NOR reached equilibrium (97.5% removal) after 60 min. The adsorption behaviours were in line with the quasi-second-order kinetic and Langmuir isotherm models, respectively. The maximum theoretical adsorption capacity reached up to 157.4 mg·g-1 at 40 °C. The thermodynamic parameters showed that the adsorption of NOR onto 3K-SCB750 was a spontaneous, endothermic, and physical process. In addition, Brunauer-Emmett-Teller analysis (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy were conducted to investigate the structural and adsorption properties of 3K-SCB750. Fourier transform infrared spectroscopy (FTIR) was also applied to understand the mechanism of adsorption of NOR onto 3K-SCB750. All of the results indicated that 3K-SCB750 had a large specific surface area of 1038.8 m2·g-1, an average pore size of 1.9 nm, and hierarchical structures with random pores and cracks for efficient removal of NOR. NOR adsorption mechanisms on 3K-SCB750 were related to the pore-filling effect and electrostatic attraction. Therefore, 3K-SCB750 biochar may be used as a promising adsorbent of antibiotics in wastewaters.

Synthesis and applications of biomass-derived porous carbon materials in energy utilization and environmental remediation

Renewable biomass and its waste are considered among the most promising applications materials owing to the depletion of fossil fuel and concerns about environmental pollution. Notably, advanced porous carbon materials derived from carbon-rich biomass precursors exhibit controllable pore structures, large surface areas, natural microstructures, and abundant functional groups. In addition, these three-dimensional structures provide sufficient reaction sites and fascinating physicochemical properties that are conducive to heteroatom doping and functional modification. This review systematically summarizes the design methods and related mechanisms of biomass-derived porous carbon materials (BDPCMs), discusses how the synthesis conditions influence the structure and performance of the carbon material, and emphasizes the importance of its use in energy utilization and environmental remediation applications. Current BDPCMs challenges and future development strategies are finally discussed to provide systematic information for further synthesis and performance optimization, which are expected to lead to novel ideas for the future development of bio-based carbon materials.

CeO2-Based Porous Carbonaceous Frameworks as Antioxidant Nanozymes for Scavenging Reactive Oxygen Species and Adsorbing Benzo[a]pyrene

Barbecue smoke, car exhaust, cigarette smoke, and other waste gases contain toxic reactive oxygen species (ROS) and polycyclic aromatic hydrocarbons (PAHs). Herein, CeO2-based porous carbonaceous frameworks (CeO2 PCFs) were explored as antioxidant nanozymes to scavenge ROS and absorb benzo[a]pyrene (B[a]P). Using cerium-based frameworks as the precursors, CeO2 PCFs were constructed by high-temperature calcination. Due to excellent superoxide dismutase-like and catalase-like activity, CeO2 PCFs could effectively eliminate superoxide radical, hydroxyl radical, and hydrogen peroxide. The 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) free radical scavenging assay had substantiated free radical scavenging ability of CeO2 PCFs. In addition, with a large surface area and porous structure, CeO2 PCFs could adsorb B[a]P efficiently. The designed CeO2 PCFs may provide a new opportunity as scavengers of ROS and absorbents of PAHs in some harmful gases.

One-step self-assembly of Fe-biochar composite for enhanced persulfate activation to phenol degradation: Different active sites-induced radical/non-radical mechanism

Persulfate (PS) activation by nanoscale zerovalent iron (nZVI) is promising for water purification, while is limited due to its easy agglomeration and oxidation. Herein, nZVI encapsuled in carbon matrix shell was synthesized via one-step carbothermal reduction. The core-shell structure effectively inhibited oxidation and agglomeration of nZVI core, and graphitized porous structures facilitated phenol binding with maximal adsorption capacity of 117.10 mg/g achieved by nZVI_0.6-BC₈₀₀. Both reactive oxygen species (SO₄^•-, O•H, O₂^•- and ¹O₂) and electron transfer process resulted in phenol decomposition. Owing to diversified active sites, the nZVI_0.6-BC₈₀₀/PS system could completely degrade phenol degradation within short time, and exhibited great adaptation to extensive pH range (3.0-9.0) and coexisting substances. Additionally, the nZVI_0.6-BC₈₀₀/PS system could maintain over 85% removal of phenol after three recycles or 50 days of storage, and was highly-efficient to different water environments, thus proposing rational design of iron-carbon catalyst with potential in water treatment.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H₂S, SO₂, Hg⁰, and CO₂) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g^-1 for H₂S, 40-182 mg g^-1 for SO₂, 80-952 μg g^-1 for Hg⁰, and 82-308 mg g^-1 CO₂, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Simultaneous adsorption of Cd(II) and degradation of OTC by activated biochar with ferrate: Efficiency and mechanism

Biochar-supported zero-valent iron nanocomposites have received much attention due to their application potential in environmental pollution remediation. However, in many occasions, zero-valent iron loading improves the electron transfer efficiency and catalytic oxidation capacity of biochar while blocking the original pore structure of biochar, limiting its application potential. In this study, a zero-valent iron composites with large SSA (865.86 m²/g) was prepared in one step using pre-pyrolysis of biochar powder and K₂FeO₄ grinding for co-pyrolysis. The processes of ZVI generation and SSA expansion during the pyrolysis were investigated. The factors affecting the removal process of Cd and OTC in water by the composites were investigated. The mechanisms of Cd fixation and OTC degradation by the composites were explored by experiments, characterization, and DFT calculations. The OTC degradation pathway was proposed by theoretical predication and LC-MS spectrometry. The results indicate that ion exchange, complexation with oxygen-containing functional groups, electrostatic attraction, and interaction with π-electrons are the main mechanisms of Cd immobilization. The degradation pathways of OTC mainly include dehydroxylation, deamination and dealkylation.

Techno-economic assessment of a novel algal-membrane system versus conventional wastewater treatment and advanced potable reuse processes: Part II

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.e., the benchmark system). The TEA study aims to estimate the levelized costs of water of individual units and integrated processes including secondary wastewater treatment, advanced water purification for potable reuse, and sludge treatment. This would provide decision-makers valuable information regarding the capital and operational costs of the innovative main system versus a typical potable water reuse treatment train, along with possible routes of cost optimization and improvements for the design of full-scale facilities. The main system consists of (i) a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water reuse and hydrothermal liquefaction (HTL) to produce bioenergy and subsequent nutrients extraction from the harvested algal biomass. The benchmark system includes (ii) an advanced water purification facility (AWPF) that consists of a conventional activated sludge biological treatment (CAS), microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), with anaerobic digestion for sludge treatment. Capital expenditures (CAPEX) and operational expenditures (OPEX) were calculated for each unit of both systems (i.e., sub-systems). Based on a 76% overall water recovery designed for the benchmark system, the water cost was estimated at $2.03/m³. The highest costs in the benchmark system were found on the CAS and the anaerobic digester, with the UV-AOP combined with GAC for hydrogen peroxide (H₂O₂) quenching as the driving factor in the increased costs of the system. The cost of the main system, based on an overall 88% water recovery, was estimated to be $1.97/m³, with costs mostly driven by the FO and SWRO membranes. With further cost reduction and optimization for FO membranes such as membrane cost, water recovery, and flux, the main system can provide a much more economically viable alternative in its application than a typical benchmark system.

Life cycle energy use and greenhouse gas emissions for a novel algal-osmosis membrane system versus conventional advanced potable water reuse processes: Part I

This study applied a life cycle assessment (LCA) methodology for a comparative environmental analysis between an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) versus a conventional potable reuse system (i.e., the benchmark system) through energy use and greenhouse gas (GHG) emissions. The objective of this study is to demonstrate that pilot-scale data coupled with LCA would provide valuable information for system optimization, integration, and improvements for the design of environmentally sustainable full-scale systems. This study also provides decision-makers valuable information regarding the energy demand and environmental impact of this innovative main system compared to a typical tried-and-true system for potable water reuse. The main system consists of a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water recovery and hydrothermal liquefaction (HTL) to recover biofuels and valuable nutrients from the harvested algal biomass. The benchmark system refers to the current industry standard technologies for potable water reuse and waste management including a secondary biological treatment, microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), as well as anaerobic digestion for sludge treatment. Respective energy and GHG emissions of both systems were normalized and compared considering 1 m³ of water recovered. Based on an overall water recovery of 76% designed for the benchmark system, the energy consumption totaled 4.83 kWh/m³, and the system was estimated to generate 2.42 kg of CO₂ equivalent/m³ with most of the emissions coming from the biological treatment. The main system, based on an overall water recovery of 88%, was estimated to consume 4.76 kWh/m³ and emit 1.49 kg of CO₂ eq/m³. The main system has high environmental resilience and can recover bioenergy and nutrients from wastewater with zero waste disposal. With the application of energy recovery devices for the HTL and the SWRO, increase in water recovery of the FO membrane, and replacement of the SWRO membrane with BWRO, the main system provides an energy-competitive and environmentally positive alternative with an energy demand of 2.57 kWh/m³ and low GHG emissions of 0.94 kg CO₂ eq/m³.

Performance and mechanism of Pb2+ and Cd2+ ions’ adsorption via modified antibiotic residue-based hydrochar

This study investigated the hydrochar-based porous carbon prepared by combining the technical route of hydrothermal carbonization (HTC) + chemical activation. The hydrochar morphology was adjusted by changing the activation reaction conditions and adding metal salts. Experiments showed that the activation of KHCO₃ significantly increased the specific surface area and pore size of the hydrochar. Besides, oxygen-rich groups on the surface of the activated hydrochar interacted with heavy metal ions to achieve efficient adsorption. The activated hydrothermal carbon adsorption capacity for Pb²⁺ and Cd²⁺ ions reached 289 and 186 mg/g, respectively. The adsorption mechanism study indicated that the adsorption of Pb²⁺ and Cd²⁺ was related to electrostatic attraction, ion exchange, and complexation reactions. The "HTC + chemical activation" technology was environmentally friendly and effectively implemented antibiotic residues. Carbon materials with high adsorption capacity can be prepared so that biomass resources can be utilized with excessive value, as a consequence presenting technical assistance for the comprehensive disposal of organic waste in the pharmaceutical industry and establishing a green and clean production system.

Lanthanum-modified polydopamine loaded Acinetobacter lwoffii DNS32 for phosphate and atrazine removal: Insights into co-adsorption and biodegradation mechanisms

A novel biobased composite was developed for the removal of phosphate (P) and atrazine from agricultural wastewater. A composite with strong P affinity and good biocompatibility, synthesized from La³⁺ and polydopamine (PDA), was immobilized onto an atrazine-degrading bacterium Acinetobacter lwoffii DNS32 (La/PDA/DNS32). Following Box-Behnken design optimization, the maximum removal rate of P (500 mg L^-1) and atrazine (100 mg L^-1) by La/PDA/DNS32 reached 28 % and 100 %, respectively. Density functional theory calculations revealed that La/PDA had more negative adsorption energy (-5.90 eV) than PDA alone and exhibited prominent electrophilic sites. Additionally, La/PDA-induced sorption of atrazine improved transmembrane transport and enhanced expression of degradation-associated genes in strain DNS32. La/PDA nanoparticles surrounding strain DNS32 provided a shielding effect and exhibited desirable biostability, thermal stability, and acid-alkaline resistance under contamination stress. This study demonstrates the promising potential of La/PDA/DNS32 in reducing the P and atrazine pollution caused by agricultural production.

Ultrahigh sorption of sulfamethoxazole by potassium hydroxide-modified biochars derived from bean-worm skin waste

Food processing of bean worm generates copious amount of skin as solid waste posing a serious environmental concern. The present study utilized bean worm skin (BWS) waste to produce KOH-modified biochars (KBWS-BCs) for the removal of sulfamethoxazole (SMX) from aqueous solution for the first time. Characterization of KBWS-BCs was systematically investigated via multiple instrumental analysis techniques. The sorption performance of KBWS-BCs as a function of solution pH, reaction time, initial SMX concentration, and reaction temperature was investigated using batch experiments. The classic kinetics and isotherm models were employed to fit the sorption data. KBWS-BCs exhibited large surface areas (3331-4742 m² g^-1) and ultrahigh sorption performance for SMX (maximum adsorption capacities of 909-2000 mg g^-1), which were comparable to those of other modified biochars and even those of well-designed materials. Thermodynamic study indicated that the sorption of SMX on KBWS-BCs was a spontaneous (△G° < 0) and exothermic (△H° < 0) process. Mechanism analysis showed that both chemisorption and physisorption were responsible for the adsorption of SMX by KBWS-BCs. Overall, recycling BWS for preparation of high-performance biochars can be a "win-win" strategy for both disposal of BWS and removal of SMX from wastewater.

Highly efficient adsorption of chromium on N, S-codoped porous carbon materials derived from paper sludge

The synergistic effect of heteroatoms is a viable method to enhance the adsorption performance of heavy metal onto carbon-based materials. However, the high cost, complex operation and a lot of pollution from the synthesis process have limited its development. Herein, a facile two-step pyrolysis method is used to prepare in situ N and S doped porous biochar from paper mill sludge for the removal of Cr(VI) from aqueous environment. The NSC-450 sample prepared under the optimum conditions has a large specific surface area of 3336.7 m² g^-1, an average pore size of 2.56 nm and a total pore volume of 2.10 cm³ g^-1, manifesting the excellent adsorption capacity of 356.25 mg g^-1 for Cr(VI). The adsorption of Cr(VI) by NSC-450 is consistent with the Langmuir isotherm and pseudo-second-order model, suggesting a spontaneous and endothermic chemisorption process. The analysis results show that the NH, graphitic nitrogen and thiophene structures have a positive effect on converting a large amount of Cr(VI) to Cr(III) by synergistic reduction, indicating obviously facilitating Cr(VI) removal compared to other sites. Therefore, in this material, the strong adsorption mechanism is mainly reductive complexation. Moreover, the effects of real water quality, anions, cations and fulvic acid on the adsorption behavior of Cr(VI) onto the NSC-450 were further investigated. The results demonstrate that the chromium removal rate remains above 82% even in actual electroplating wastewater, suggesting NSC-450 has great practical application prospect. This work offered a feasible method for high-value utilization of sludge, but also provided a novel perspective for the future design of heteroatom-doped carbon materials for promoting to eliminate hexavalent chromium from water environment.

Pinecone-derived magnetic porous hydrochar co-activated by KHCO3 and K2FeO4 for Cr(VI) and anthracene removal from water

Herein, magnetic porous pinecone-derived hydrochar (MPHC_MW) co-activated by KHCO₃ and K₂FeO₄ through one-step microwave-assisted pyrolysis was innovatively synthesized for hexavalent chromium (Cr(VI)) and anthracene (ANT) removal from water. The analyses of characterization consequences and co-activation mechanisms not merely proved the high specific surface area (703.97 m²/g) and remarkable microporous structures of MPHC_MW caused by the synergistic chemical activation of KHCO₃ and K₂FeO₄, but also testified successful loading of Fe⁰ and Fe₃O₄ on MPHC_MW by the process of carbothermal reduction between K₂FeO₄ and carbon matrix of hydrochar. The resultant MPHC_MW possessed pH-dependence for Cr(VI), while adsorption for ANT was hardly impacted by the pH of solution. Moreover, the adsorption processes of MPHC_MW could attain equilibrium within 60 min for Cr(VI) and 30 min for ANT with multiple kinetics, and the corresponding adsorption capacity for Cr(VI) and ANT was 128.15 and 60.70 mg/g, respectively. Additionally, the adsorption percentages of MPBC_MW for Cr(VI)/ANT was maintained at 87.87/82.64% after three times of adsorption-desorption cycles. Furthermore, pore filling, complexation, electrostatic interaction, reduction and ion exchange were testified to enhance the removal of Cr(VI), while the ANT removal was achieved via π-π stacking, complexation, pore filling and hydrogen bonding force.

Combining biological and chemical methods to disassemble of cellulose from corn straw for the preparation of porous carbons with enhanced adsorption performance

In this study, we used a combination of chemical and biological pretreatment methods to extract cellulose from corn straw with a relative content of 92.40%. The adsorption performance and mechanism of the prepared porous carbon were investigated using synthetic dye malachite green (MG) and antibiotic tetracycline hydrochloride (TC) as adsorption models. The kinetic studies suggested that the adsorption followed the pseudo-second-order model and Bangham model. The Freundlich isotherm model fitted the adsorption data best for both MG and TC. The thermodynamic studies showed that the adsorption of MG and TC by adsorbents were spontaneous and endothermic in nature. In addition, the adsorption performance was maintained at 50% of the original value after five cycles. More importantly, this method not only improved the adsorption performance of prepared porous carbon materials but also provides a reference for the application of other lignocellulosic materials for cellulose extraction.

Facile preparation of magnetic porous biochars from tea waste for the removal of tetracycline from aqueous solutions: Effect of pyrolysis temperature

Pyrolysis process significantly influences the physicochemical properties and potential application of magnetic porous biochars (MPBCs). However, the effects of pyrolysis temperature on the properties of MPBCs as well as substantial adsorption are still unclear. This study reported a facile method to obtain the MPBC from tea waste via pyrolysis of a mixture of hydrochar, KHCO₃, and FeCl₃·6H₂O under different temperatures (500-800 °C), and explored further the adsorption toward tetracycline (TC). Results showed pyrolysis temperature obviously influenced the physicochemical properties of MPBCs, and MPBC pyrolyzed at 700 °C (MPBC-700) has a highest specific surface area (1066 m² g^-1) and pore volume (2.693 cm³ g^-1). However, the adsorption potential increased consistently from 59.35 mg g^-1 for MPBC-500 to 333.22 mg g^-1 for MPBC-800, suggesting that the surface area and pore volume were not the only factors determining TC adsorption. Further analysis showed that the pore-filling, π-π interaction, complexation, and hydrogen bonding contributed together to TC adsorption. Moreover, all MPBCs possessed a high saturation magnetization, indicating the easy separation by an external magnet. Therefore, MPBCs (especially at 700 °C) can act as the excellent adsorbents for contaminant removal due to their high separation, adsorption, and reuse performance.

Adsorption of polycyclic aromatic hydrocarbons from wastewater using graphene-based nanomaterials synthesized by conventional chemistry and green synthesis: A critical review

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants formed mainly by the incomplete combustion of organic matter, such as oil, gas and coal. The presence of PAHs can cause irreparable damage to the environment and living beings, which has generated a global concern with the short and long term risks that the emission of these pollutants can cause. Many technologies have been developed in the last decades aiming at the identification and treatment of these compounds, mainly, the PAHs from wastewater. This review features an overview of studies on the main methods of PAHs remediation from wastewater, highlighting the adsorption processes, through the application of different adsorbent nanomaterials, with a main focus on graphene-based nanomaterials, synthesized by conventional and green routes. Batch and fixed-bed adsorptive processes were evaluated, as well as, the mechanisms associated with such processes, based on kinetic, equilibrium and thermodynamic studies. Based on the studies analyzed in this review, green nanomaterials showed higher efficiency in removing PAHs than the conventional nanomaterials. As perspectives for future research, the use of green nanomaterials has shown to be sustainable and promising for PAHs remediation, so that further studies are needed to overcome the possible challenges and limitations of green synthesis methodologies.

N,Cl-Codoped Carbon Dots from Impatiens balsamina L. Stems and a Deep Eutectic Solvent and Their Applications for Gram-Positive Bacteria Identification, Antibacterial Activity, Cell Imaging, and ClO- Sensing

In this study, we first synthesized metal-free N,Cl-doped carbon dots (N,Cl-CDs) using Impatiens balsamina L. stems as green precursors in a deep eutectic solvent (DES). The obtained N,Cl-CDs were characterized through transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, fluorescence (FL) spectroscopy, and ultraviolet (UV) spectroscopy. In addition to the common features of carbon dots (CDs), such as high light stability, small size, low toxicity, good aqueous solubility, and favorable biocompatibility, these N,Cl-CDs exhibited excellent recognition and selectivity for Gram-positive bacteria by doping with N and Cl elements using DES. The N,Cl-CDs with positive charge cannot only differentiate Gram-positive bacteria by selective fluorescence imaging but also have antibacterial effects on Gram-positive bacteria. Through potential, ROS, and morphological analyses of bacteria before and after treatment with N,Cl-CDs, the antibacterial mechanisms of bacteriostasis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella were explored. In addition, N,Cl-CDs demonstrated low cytotoxicity and good cell imaging ability in cancer and normal cells. Moreover, they can be used as a fluorescence sensor for the detection of ClO- with a detection range from 100 nM to 40 μM and a limit of detection (LOD) of 30 nM. In summary, the prepared N,Cl-CDs could be applied as environmentally friendly Gram-positive bacterial identification and antibacterial agents. Additionally, their cell imaging and ClO- detection abilities were outstanding.

Unraveling the Ion Adsorption Kinetics in Microporous Carbon Electrodes: A Multiscale Quantum-Continuum Simulation and Experimental Approach

Understanding sorption in porous carbon electrodes is crucial to many environmental and energy technologies, such as capacitive deionization (CDI), supercapacitor energy storage, and activated carbon filters. In each of these examples, a practical model that can describe ion electrosorption kinetics is highly desirable for accelerating material design. Here, we proposed a multiscale model to study the ion electrosorption kinetics in porous carbon electrodes by combining quantum mechanical simulations with continuum approaches. Our model integrates the Butler-Volmer (BV) equation for sorption kinetics and a continuously stirred tank reactor (CSTR) formulation with atomistic calculations of ion hydration and ion-pore interactions based on density functional theory (DFT). We validated our model experimentally by using ion mixtures in a flow-through electrode CDI device and developed an in-line UV absorption system to provide unprecedented resolution of individual ions in the separation process. We showed that the multiscale model captures unexpected experimental phenomena that cannot be explained by the traditional ion electrosorption theory. The proposed multiscale framework provides a viable approach for modeling separation processes in systems where pore sizes and ion hydration effects strongly influence the sorption kinetics, which can be leveraged to explore possible strategies for improving carbon-based and, more broadly, pore-based technologies.

Facile modification of hydrochar derived from cotton straw with excellent sorption performance for antibiotics: Coupling DFT simulations with experiments

This study aimed to investigate the sorption of tetracycline (TC) and norfloxacin (NOR) by modified cotton straw hydrochars (CSHC), which would enable the agricultural waste to be processed and recycled. Three kinds of hydrochars were prepared by H₂SO₄, KOH and KMnO₄ modification, showed obvious differences in structures and surface functional groups. The sorption processes contain film diffusion, intraparticle diffusion, and equilibrium. The interaction mechanism between hydrochar and antibiotics include π-π stacking, hydrogen bond, and electrostatic interaction. KMnO₄-modified hydrochar had the largest sorption capacity for TC (58.09 mg/g), while H₂SO₄-modified hydrochar had the largest sorption capacity for NOR (49.64 mg/g). Density functional calculations (DFT) results confirmed that the sorption capacity between hydrochar (HC) and TC was larger than that between HC and NOR. During the sorption process, the TC and NOR were regarded as electron acceptor and electron donor. Generally, CSHC-KMnO₄ and CSHC-H₂SO₄ may be simply prepared and have the potential to eliminate antibiotics from water.

Effect of carbonization methods on the properties of tea waste biochars and their application in tetracycline removal from aqueous solutions

The properties of biochars and their adsorption performance are highly dependent on the carbonation methods. In this study, five carbonation methods, namely, hydrothermal treatment (HT), direct carbonization (BC), carbonization of hydrochar (HBC), KHCO₃ activation carbonation (KBC), and KHCO₃ activation carbonation of hydrochar (KHBC), were adopted to prepare tea waste biochars. Adsorption behaviors and mechanisms toward tetracycline (TC) by biochar in the aquatic environment were investigated. The results showed that carbonation methods significantly influence the morphology, carbon structure, chemical composition, and functional groups of the biochars based on the characterization of surface area and pore volume analysis, Fourier Transform Infrared Spectroscopy, Raman spectrum, Scanning Electron Microscope, Transmission Electron Microscope, X-ray photoelectron spectroscopy, X-Ray Diffraction, and elemental analysis. Combination of hydrothermal treatment with KHCO₃ activation can significantly increase the surface area and enlarge the pore structure of biochar (KHBC and KBC). The BET of KHCO₃-activated BCs nearly increased 280 times (KHBC: 1350.80 m² g^-1; KBC: 1405.06 m² g^-1). BET, total pore volume and micropores volume of biochar has a positive influence on TC adsorption capacity. In addition, all adsorption processes can be well fitted by Langmuir and pseudo-second-order kinetic models. The maximum adsorption capacity of KHCO₃-activated BCs nearly increased approximately 40 times (KHBC: 451.45 mg g^-1; KBC: 425.17 mg g^-1). The dominant mechanisms of biochar-adsorbed TC were pore-filling effect and π-π interactions, followed by hydrogen bonds and electrostatic interactions. Therefore, KHBC has the potential to act as sorbents for TC removal from aquatic environment.

Characterization and utilization of biochars derived from five invasive plant species Bidens pilosa L., Praxelis clematidea, Ipomoea cairica, Mikania micrantha and Lantana camara L. for Cd2+ and Cu2+ removal

Exotic invasive plants endanger the integrity of agricultural and natural systems throughout the world. Thus, the development of cost-effective and economic application of invasive plants is warranted. Here, we characterized fifteen biochars derived from five invasive plants at different temperatures (300, 500, and 700 °C) by determining their yield, ash content, pH, CEC, surface area, elementary composition, functional groups, and mineral composition. We conducted batch adsorption experiments to investigate the adsorption capacity and efficiency for Cd²⁺ and Cu²⁺ in wastewater. Our results suggest that all invasive plants are appropriate for biochar production, temperature and plant species had interacting effects on biochar properties, and the biochars pyrolyzed at 500 and 700 °C exhibited high metal adsorption capacity in neutral (pH = 7) solutions. The adsorption kinetics can be explained adequately by a pseudo-second-order model. BBC500 (Bidens pilosa L. derived biochar at 500 °C) and MBC500 (Mikania micrantha) exhibited higher metal equilibrium adsorption capacities (38.10 and 38.02 mg g^-1 for Cd²⁺, 20.01 and 20.10 mg g^-1 for Cu²⁺) and buffer abilities to pH than other biochars pyrolyzed at 500 °C. The Langmuir model was a better fit for IBC500 (Ipomoea cairica), MBC500, and LBC500 (Lantana camara L.) compared to the Freundlich model, whereas the opposite was true for BBC500 and PBC500 (Praxelis clematidea). These results suggest that the adsorption of metals by IBC500, MBC500, and LBC500 was mainly monolayer adsorption, while that by BBC500 and PBC500 was mainly chemical adsorption. Our results are important for the utilization and control of invasive plants as well as the decontamination of aqueous pollution.

Quantitative proteomic analysis to reveal expression differences for butanol production from glycerol and glucose by Clostridium sp. strain CT7

Clostridium sp. strain CT7 is a new emerging microbial cell factory with high butanol production ratio owing to its non-traditional butanol fermentation mode with uncoupled acetone and 1,3-propanediol formation. Significant changes of metabolic products profile were shown in glycerol- and glucose-fed strain CT7, especially higher butanol and lower volatile fatty acids (VFAs) production occurred from glycerol-fed one. However, the mechanism of this interesting phenomenon was still unclear. To better elaborate the bacterial response towards glycerol and glucose, the quantitative proteomic analysis through iTRAQ strategy was performed to reveal the regulated proteomic expression levels under different substrates. Proteomics data showed that proteomic expression levels related with carbon metabolism and solvent generation under glycerol media were highly increased. In addition, the up-regulation of hydrogenases, ferredoxins and electron-transferring proteins may attribute to the internal redox balance, while the earlier triggered sporulation response in glycerol-fed media may be associated with the higher butanol production. This study will pave the way for metabolic engineering of other industrial microorganisms to obtain efficient butanol production from glycerol.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.

KOH-activated porous biochar with high specific surface area for adsorptive removal of chromium (VI) and naphthalene from water: Affecting factors, mechanisms and reusability exploration

Herein, a high-performance porous biochar described as PBC_KOH was successfully synthesized by two-step pyrolysis of corn straw with chemical activation of KOH, and was employed for the elimination of Cr(VI) and naphthalene (NAP) from water. Benefiting from KOH activation, the PBC_KOH was found to possess huge specific surface area of 2183.80 m²/g and many well-developed micropores with average particle size of 2.75 nm and main pore diameters distribution from 1 to 2 nm. The PBC_KOH presented an excellent adsorption performance with a theoretical monolayer uptake of 116.97 mg/g for Cr(VI) and a heterogeneous adsorption capacity of 450.43 mg/g for NAP. The uptake equilibrium was attained within about 120 min for Cr(VI), while about 180 min for NAP following avrami fractional-order model, revealing the existence of multiple kinetics during the adsorption. The thermodynamic results showed that the uptake of both Cr(VI) and NAP occurred spontaneously (-ΔG°), while in an endothermic nature for Cr(VI) (+ΔH°) and an exothermic characteristic for NAP (-ΔH°) with different randomness. Furthermore, the PBC_KOH was believed to enhance the Cr(VI) adsorption mainly through the combination of electrostatic attraction, complexation, ion exchange and reduction action, while achieving the high NAP uptake by pore filling and π-π stacking interactions.

Cyan color-emitting nitrogen-functionalized carbon nanodots (NFCNDs) from Indigofera tinctoria and their catalytic reduction of organic dyes and fluorescent ink applications

The present study reports the synthesis of nitrogen-functionalized carbon nanodots (NFCNDs) by a low-cost hydrothermal method using the leaf extract of Indigofera tinctoria as a novel carbon precursor.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

Enhanced phosphate scavenging with effective recovery by magnetic porous biochar supported La(OH)3: Kinetics, isotherms, mechanisms and applications for water and real wastewater

Herein, La(OH)₃ decorated magnetic porous biochar (MPBC) was synthesized via KHCO₃ activation and hydrothermal processes. The La-to-MPBC mass ratio of 3:1 described as La₃-MPBC possessed a monolayer phosphate adsorption capacity of 116.08 mg/g across a pH range of 3.0-6.0 with fast attainment of adsorption equilibrium in 150 min. Moreover, the phosphate adsorption was substantially stable during the interference of various co-existing ions with over 92% of phosphate removal and 77% of desorption efficiency maintained after four recycles. And La₃-MPBC was easily separated by magnet force with negligible La and Fe leakages within the pH range of 3.0-10.0. Furthermore, La₃-MPBC was supported to achieve phosphate binding through the synergistic actions of electrostatic attraction, ligand exchange, inner-sphere complexation and weak precipitation. Significantly, La₃-MPBC exhibited a high performance for decontaminating low-concentration phosphate to meet regulatory requirements. All these results suggested La₃-MPBC to be an ideal candidate for phosphate removal in real applications.