Fabrication and characterization of hydrophilic corn stalk biochar-supported nanoscale zero-valent iron composites for efficient metal removal

Nonmetallic modified zero-valent iron for remediating halogenated organic compounds and heavy metals: A comprehensive review

Zero Valent Iron (ZVI), an ideal reductant treating persistent pollutants, is hampered by issues like corrosion, passivation, and suboptimal utilization. Recent advancements in nonmetallic modified ZVI (NM-ZVI) show promising potential in circumventing these challenges by modifying ZVI's surface and internal physicochemical properties. Despite its promise, a thorough synthesis of research advancements in this domain remains elusive. Here we review the innovative methodologies, regulatory principles, and reduction-centric mechanisms underpinning NM-ZVI's effectiveness against two prevalent persistent pollutants: halogenated organic compounds and heavy metals. We start by evaluating different nonmetallic modification techniques, such as liquid-phase reduction, mechanical ball milling, and pyrolysis, and their respective advantages. The discussion progresses towards a critical analysis of current strategies and mechanisms used for NM-ZVI to enhance its reactivity, electron selectivity, and electron utilization efficiency. This is achieved by optimizing the elemental compositions, content ratios, lattice constants, hydrophobicity, and conductivity. Furthermore, we propose novel approaches for augmenting NM-ZVI's capability to address complex pollution challenges. This review highlights NM-ZVI's potential as an alternative to remediate water environments contaminated with halogenated organic compounds or heavy metals, contributing to the broader discourse on green remediation technologies.

Effect of Mn2+ on RO membrane organic fouling: Insights into the complexation and interfacial interaction

RO process is commonly used to treat and reuse manganese-containing industrial wastewater. Nevertheless, even after undergoing multi-stage treatment, the secondary biochemical effluent still exhibits a high concentration of Mn2+ coupled with organics entering the RO system, leading to membrane fouling. In this work, we systematically analyze the RO membrane organic fouling processes and mechanisms, considering the coexistence of Mn2+ with humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA) and their mixtures (HBS). The impact of Mn2+ on membrane fouling was HBS > SA > HA > BSA, controlling polysaccharide pollutant concentrations should be a priority for mitigating membrane fouling. In the presence of Mn2+ with HA, SA, or HBS, membrane fouling is primarily attributed to the complexation of organics and Mn2+ and the facilitation of interfacial interaction energy. RO membrane BSA fouling was not directly affected by Mn2+, the addition of Mn2+ induced a salting-out effect, leading to the deposition of BSA in a single molecular on the membrane. Simultaneously, adhesion energy hinders the deposition of BSA on the membrane, resulting in milder membrane fouling. This study provided the theoretical basis and suggestions for RO membrane organic fouling control in the presence of Mn2+.

Responses of nitrobenzene removal performance and microbial community by modified biochar supported zerovalent iron in anaerobic soil

Biochar-supported ZVI have received increasing attention for their potential to remove nitrobenzene in groundwater and soil. However, the capacity of this material to enhance the biological reduction of nitrobenzene and alter microbial communities in anaerobic groundwater have not been explored. In this study, the nitrobenzene removal performance and mechanism of modified biochar-supported zerovalent iron (ZVI) composites were explored in anaerobic soil. The results showed that the 700 °C biochar composite enhanced the removal of nitrobenzene and inhibited its release from soil to the aqueous phase. NaOH-700-Fe50 had the highest removal rate of nitrobenzene, reaching 64.4%. However, the 300 °C biochar composite inhibited the removal of nitrobenzene. Microbial degradation rather than ZVI-mediated reduction was the main nitrobenzene removal pathway. The biochar composites changed the richness and diversity of microbial communities. ZVI enhanced the symbiotic relationship between microbial genera and weakened competition between soil microbial genera. In summary, the 700 °C modified biochar composite enhanced the removal of nitrobenzene by increasing microbial community richness and diversity, by upregulating functional genes, and by promoting electron transfer. Overall, the modified biochar-supported ZVI composites could be used for soil remediation, and NaOH-700-Fe50 is a promising composite material for the on-site remediation of nitrobenzene-contaminated groundwater.

Selective adsorption of antibiotics from human urine using biochar modified by dimethyl sulfoxide, deep eutectic solvent, and ionic liquid

Antibiotics present in human urine pose significant challenges for the use of urine-based fertilizers in agriculture. This study introduces a novel two-stage approach utilizing distinct biochar types to mitigate this concern. Initially, a modified biochar selectively adsorbed azithromycin (AZ), ciprofloxacin (CPX), sulfamethoxazole (SMX), trimethoprim (TMP), and tetracycline (TC) from human urine. Subsequently, a separate pristine biochar was employed to capture nutrients. Biochar, derived from sewage sludge and pyrolyzed at 550 and 700 °C, was modified using dimethyl sulfoxide, deep eutectic solvent, and ionic liquid to enhance antibiotic removal in the first stage. The modifications introduced hydrophilic functional groups (-OH/-COOH), which favor antibiotic adsorption. Adsorption kinetics followed the pseudo-second-order model, with the Langmuir isotherm model best describing the adsorption data. The maximum adsorption capacities for AZ, CPX, SMX, TMP, and TC after the modification were 196.08, 263.16, 81.30, 370.37, and 833.33 μg/g, respectively. Pristine biochar exhibited a superior ammonia adsorption capacity compared to the modified biochar. Hydrogen bonding, electrostatic attraction, and chemisorption drove antibiotic adsorption on the modified biochar. Regeneration efficiency declined due to solvent accumulation and potential byproduct formation on the biochar surface (<30% removal capacity after three cycles). This study presents innovative biochar modification strategies for selective antibiotic adsorption, laying the groundwork for environmentally friendly urine-based fertilizers in agriculture.

Insights into the pH-dependent mechanism of peracetic acid activation by biochar-supported zero-valent iron/cobalt bimetallic nanoparticles: The shift of reactive sites and the dual role of hydrogen peroxide

The peracetic acid (PAA)-based water purification process is often controlled by the solution pH. Herein, we explored the usage of biochar (BC) supported zero-valent iron/cobalt nanoparticles (Fe/Co@BC) for triggering PAA oxidation of sulfamethazine (SMT), and discovered the PAA activation mechanisms at different pHs. Fe/Co@BC exhibited extraordinary PAA activation efficiency over the pH range of 3.0-8.2, effectively broadening the working pH of the zero-valent iron nanoparticles (NZVI)-PAA process. Specifically, the SMT removal efficiency increased by 8.3 times in Fe/Co@BC-PAA system compared to the NZVI-PAA system at pH 8.2. Besides, the leaching and recycling experiments indicated the improved stability and reusability of the materials. For the mechanism study, the main reactive species was •OH under acidic conditions and R-O•/Fe(IV) under neutral/alkaline conditions. More interestingly, the reactive sites on Fe/Co@BC shifted from Fe species to Co species as pH increased, and the role of H2O2 in this reaction system also shifted from a radical precursor to a radical scavenger with increasing pH. This study highlights the distinct mechanism of PAA activation by bimetallic composites under different pH conditions and provides a new efficient approach for PAA activation to degrade organic contaminants.

A comprehensive review of the "black gold catalysts" in wastewater treatment: Properties, applications and bibliometric analysis

A significant amount of effort has been devoted to the utilization of biochar-based catalysts in the treatment of wastewater. By virtue of its abundant functional groups and high specific surface area, biochar holds significant promise as a catalyst. This article presents a comprehensive systematic review and bibliometric analysis covering the period from 2009 to 2024, focusing on the restoration of wastewater through biochar catalysis. The production, activation, and functionalization techniques employed for biochar are thoroughly examined. In addition, the application of advanced technologies such as advanced oxidation processes (AOPs), catalytic reduction reactions, and biochemically driven processes based on biochar are discussed, with a focus on elucidating the underlying mechanisms and how surface functionalities influence the catalytic performance of biochar. Furthermore, the potential drawbacks of utilizing biochar are also brought to light. To emphasize the progress being made in this research field and provide valuable insights for future researchers, a scientometric analysis was conducted using CiteSpace and VOSviewer software on 595 articles. Hopefully, this review will enhance understanding of the catalytic performance and mechanisms pertaining to biochar-based catalysts in pollutant treatment while providing a perspective and guidelines for future research and development efforts in this area.

Superb green cycling strategies for microbe-Fe0 neural network-type interaction: Harnessing eight key genes encoding enzymes and mineral transformations to efficiently treat PFOA

To address time-consuming and efficiency-limited challenges in conventional zero-valent iron (ZVI, Fe0) reduction or biotransformation for perfluorooctanoic acid (PFOA) treatment, two calcium alginate-embedded amendments (biochar-immobilized PFOA-degrading bacteria (CB) and ZVI (CZ)) were developed to construct microbe-Fe0 high-rate interaction systems. Interaction mechanisms and key metabolic pathways were systematically explored using metagenomics and a multi-process coupling model for PFOA under microbe-Fe0 interaction. Compared to Fe0 (0.0076 day-1) or microbe (0.0172 day-1) systems, the PFOA removal rate (0.0426 day-1) increased by 1.5 to 4.6 folds in the batch microbe-Fe0 interaction system. Moreover, Pseudomonas accelerated the transformation of Fe0 into Fe3+, which profoundly impacted PFOA transport and fate. Model results demonstrated microbe-Fe0 interaction improved retardation effect for PFOA in columns, with decreased dispersivity a (0.48 to 0.20 cm), increased reaction rate λ (0.15 to 0.22 h-1), distribution coefficient Kd (0.22 to 0.46 cm3∙g-1), and fraction f´(52 % to 60 %) of first-order kinetic sorption of PFOA in microbe-Fe0 interaction column system. Moreover, intermediates analysis showed that microbe-Fe0 interaction diversified PFOA reaction pathways. Three key metabolic pathways (ko00362, ko00626, ko00361), eight functional genes, and corresponding enzymes for PFOA degradation were identified. These findings provide insights into microbe-Fe0 "neural network-type" interaction by unveiling biotransformation and mineral transformation mechanisms for efficient PFOA treatment.

High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.

Advances in Fe-modified lignocellulosic biochar: Impact of iron species and characteristics on wastewater treatment

Lignocellulosic biomass is an attractive feedstock for biochar production owing to its high abundance and renewability. Various modified biochars have been extensively studied for wastewater treatment to improve the physical and chemical properties of lignocellulosic biochar (L-BC). Particularly, Fe-modified L-BCs have garnered attention owing to the abundance and eco-friendliness of Fe and the outstanding ability to remove various organic and inorganic contaminants via adsorption, oxidation, reduction, and catalytic reactions. Different iron species (e.g., Fe(0), Fe (hydr)oxide, Fe sulfide, and Fe-Metal) are formed during the preparation of Fe-L-BCs, which can completely differentiate the physical and chemical properties of BCs. This review discusses the advances in the synthesis of different Fe-L-BCs, specific changes in the physical and chemical properties of Fe-L-BCs upon Fe addition, and their impacts on wastewater treatment. The results of this review can demonstrate the unique advantages and drawbacks of Fe-L-BCs for the removal of different types of pollutants.

Competitive adsorption mechanisms of Cd(II), Cu(II) and Pb(II) on bioinspired mesoporous silica revealed by complementary adsorption/isothermal titration calorimetry studies

This study presents the adsorption properties of a bioinspired grafted mesoporous silica material and the competitive effects between Cd(II) or Cu(II) and Pb(II) during the adsorption process. Glutathione, a natural antioxidant known for its metal binding properties, has been successfully grafted to SBA-15 mesoporous silica and the optimum adsorption parameters were determined. This original and multidisciplinary approach combines classical adsorption studies with thermodynamic investigations to understand the adsorption behavior of Cd(II), Cu(II) and Pb(II) on this material. To this end, isothermal titration calorimetry (ITC) has been used to elucidate the mechanisms of single-metal and two-metal adsorption. The results showed affinity in the order Pb(II) > Cu(II) > Cd(II) in single metal systems. Cd(II) adsorption relied mainly on physical contributions while Cu(II) and Pb(II) adsorption was shown to be chemically driven. Two-metal systems highlighted that Cd(II) and Pb(II) are adsorbed on the same coordination sites, whereas Cu(II) and Pb(II) are adsorbed on different sites. The material showed good selectivity and encouraging results were obtained on real effluents.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

Enhanced adsorption performance of oxytetracycline in aqueous solutions by Mg-Fe modified suaeda-based magnetic biochar

Oxytetracycline (OTC) in the waste water can be removed by biochar adsorption. How to separate the biochar adsorbed antibiotics from the wastewater was also a problem. The nontoxic magnetic biochar was prepared from Suaeda biochar (800SBC) by mafic bimetal modification, and used for the removal of OTC. The results of XRD and VSM indicated that the main composition of biochar was ferrite. Then through batch adsorption experiments, the adsorption kinetics, isothermal adsorption, thermodynamics, and coexisting ion and adsorbent regeneration experiments were studied. Through the fitting of the adsorption model, it was found that Mg-Fe@800SBC(1:1) and 800SBC belonged to chemisorption. 800SBC was consistent with the Langmuir model, mainly monolayer adsorption, and Mg-Fe@800SBC(1:1) was consistent with the Freundlich model, mainly multilayer adsorption. The adsorption processes of the two materials were spontaneous, endothermic and entropic decreasing processes. The maximum adsorption capacity of the Mg-Fe@800SBC(1:1) for OTC from the Sips L-F model was 82.83 mg/g. Through various characterizations of magnetic biochar, it was found that the adsorption mechanism of the modified biochar included the hydrogen bonds between the oxygen-containing functional group of biochar and the -NH2 group of OTC, π-π EDA interaction, electrostatic attraction and complexation. Coexistence anions (CO32- and PO43-) have a negative effect on the adsorption process.

Effect and mechanism of kaolinite loading amorphous zero-valent iron to stabilize cadmium in soil

Amorphousness effectively improves the electron transfer rate of zero-valent iron. In this study, a novel kaolinite loading amorphous zero-valent iron composite (K-AZVI) was prepared and applied to the remediation of soils with cadmium (Cd) pollution concentrations of 20, 50, and 100 mg/kg respectively. The results showed that the application of K-AZVI increased the pH and cation exchange capacity (CEC) of soil, and decreased the dissolved organic carbon (DOC) and organic matter (OM) of soil, thus indirectly promoting the adsorption of Cd in the soil. After 28 days of stabilization, the stabilizing efficiency of K-AZVI on the water-soluble Cd content in soil reached 98.72 %. Under the amendment of 0.25 %-1.0 % (w/w), the available Cd content in 20-100 mg/kg contaminated soil decreased by 46.47 %-62.23 %, 24.10 %-41.52 %, and 16.09 %-30.51 % respectively compared with CK. More importantly, the addition of K-AZVI promoted the transformation of 33.18 %-48.42 % exchangeable fraction (EXC) to 10.09 %-20.14 % residual fraction (RES), which increased the abundance and diversity of soil bacterial communities. Comprehensive risk assessment showed that adding 1.0 % K-AZVI provided the best remediation on contaminated soil. In addition, the results of scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) of K-AZVI before and after the reaction showed that the stabilization mechanism of K-AZVI to Cd in soil is mainly the stable metal species (Cd(OH)2, CdO and CdFe2O4) formed by the direct complexation and coprecipitation of a large number of iron oxides formed by the rapid corrosion of amorphous zero-valent iron (AZVI). Overall, this work provides a promising approach to the remediation of Cd-contaminated soil using K-AZVI composites.

Adverse effects of iron-based nanoparticles on freshwater phytoplankton Scenedesmus armatus and Microcystis aeruginosa strains

Zero-valent nano-iron particles (nZVI) are increasingly present in freshwater aquatic environments due to their numerous applications in environmental remediation. However, despite the broad benefits associated with the use and development of nZVI nanoparticles, the potential risks of introducing them into the aquatic environment need to be considered. Special attention should be focused on primary producer organisms, the basal trophic level, whose impact affects the rest of the food web. Although there are numerous acute studies on the acute effects of these nanoparticles on photosynthetic primary producers, few studies focus on long-term exposures. The present study aimed at assessing the effects of nZVI on growth rate, photosynthesis activity, and reactive oxygen activity (ROS) on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa. Moreover, microcystin production was also evaluated. These parameters were assessed on both organisms singly exposed to 72 h-effective nZVI concentration for 10% maximal response for 28 days. The results showed that the cell growth rate of S. armatus was initially significantly altered and progressively reached control-like values at 28 days post-exposure, while M. aeruginosa did not show any significant difference concerning control values at any time. In both strains dark respiration (R) increased, unlike net photosynthesis (Pn), while gross photosynthesis (Pg) only slightly increased at 7 days of exposure and then became equal to control values at 28 days of exposure. The nZVI nanoparticles generated ROS progressively during the 28 days of exposure in both strains, although their formation was significantly higher on green algae than on cyanobacteria. These data can provide additional information to further investigate the potential risks of nZVI and ultimately help decision-makers make better informed decisions regarding the use of nZVI for environmental remediation.

Insights into the electron activation mechanisms at the micro level by nano zero-valent iron supported by molybdenum disulfide (nZVI@MD) from preparation to application

Both molybdenum disulfide (MoS2) and nano zero-valent iron (nZVI) exhibit excellent adsorption abilities. However, the constrained conductivity of MoS2 and the lack of selectivity of nZVI for electron transfer still pose challenges. In this study, we designed a series of novel nano zero-valent iron supported by molybdenum disulfide composites (nZVI@MD) with multiple electron-rich active sites, including iron dopant replacement, iron atom intercalation and exposed Mo4+, for effective removal of Cr(VI). Results showed that preparation temperature and the amount of MoS2 added were identified as the two most significant factors affecting the reduction properties of nZVI@MD. Systematic experiments revealed that the nZVI@MD exhibited good anti-interference performance, stability and reusability due to its excellent electron selectivity. Characterization results exhibited that iron atoms replaced the sulfur vacancies in MoS2 and inserted into an intercalation of MoS2 during the preparation process. The mechanisms underlying the uptake of Cr(VI) by nZVI@MD can be proposed as follows: (i) electrostatic interactions, (ii) reduction reaction, and (iii) co-precipitation involving Fe-O-Cr. Furthermore, nZVI@MD exhibited excellent electron activity, hydrophilicity and oxidation resistance, confirmed by density functional theory (DFT) calculations. This work provided new strategies and mechanistic insights for the rational design of adsorbents.

Remediation of soil polluted with Pb and Cd and alleviation of oxidative stress in Brassica rapa plant using nanoscale zerovalent iron supported with coconut-husk biochar

Accumulation of toxic elements by plants from polluted soil can induce the excessive formation of reactive oxygen species (ROS), thereby causing retarded plants' physiological attributes. Several researchers have remediated soil using various forms of zerovalent iron; however, their residual impacts on oxidative stress indicators and health risks in leafy vegetables have not yet been investigated. In this research, nanoscale zerovalent iron supported with coconut-husk biochar (nZVI-CHB) was synthesized through carbothermal reduction process using Fe2O3 and coconut-husk. The stabilization effects of varying concentrations of nZVI-CHB and CHB (250 and 500 mg/kg) on cadmium (Cd) and lead (Pb) in soil were analyzed, and their effects on toxic metals induced oxidative stress, physiological properties, and antioxidant defence systems of the Brassica rapa plant were also checked. The results revealed that the immobilization of Pb and Cd in soil treated with CHB was low, leading to a higher accumulation of metals in plants grown. However, nZVI-CHB could significantly immobilize Pb (57.5-62.12%) and Cd (64.1-75.9%) in the soil, leading to their lower accumulation in plants below recommended safe limits and eventually reduced carcinogenic risk (CR) and hazard quotient (HQ) for both Pb and Cd in children and adults below the recommended tolerable range of <1 for HQ and 10-6 - 10-4 for CR. Also, a low dose of nZVI-CHB significantly mitigated toxic metal-induced oxidative stress in the vegetable plant by inhibiting the toxic metals uptake and increasing antioxidant enzyme activities. Thus, this study provided another insightful way of converting environmental wastes to sustainable adsorbents for soil remediation and proved that a low-dose of nZVI-CHB can effectively improve soil quality, plant physiological attributes and reduce the toxic metals exposure health risk below the tolerable range.

Simultaneous adsorption of Cd and As by a novel coal gasification slag based composite: Characterization and application in soil remediation

Cadmium (Cd) and arsenic (As) co-contamination has become increasingly serious in China agricultural soil due to rapid industrialization and urbanization. The opposite geochemical behaviors of Cd and As pose huge challenges for developing a material for their simultaneous immobilization in soils. Coal gasification slag (CGS) as a by-product of coal gasification process, is always dumped into a local landfill, which has a negative impact on environment. Few reports have been available on applying CGS as a material to immobilize simultaneously multiple soil heavy metals. A series of iron-modified coal gasification slag (IGS) composites IGS3/5/7/9/11 (with different pH values) were synthesized by alkali fusion and iron impregnation. After modification, carboxyl groups were activated, and Fe was successfully loaded onto the surface of IGS in the form of FeO and Fe₂O₃. The IGS7 exhibited the best adsorption capacity with the maximum Cd and As adsorption capacity of 42.72 mg/g and 35.29 mg/g, respectively. The Cd was mainly adsorbed through electrostatic attraction and precipitation, while the As through complexation with iron (hydr)oxides. IGS7 significantly reduced the bioavailability of Cd and As in soil with Cd bioavailability reduced from 1.17 mg/kg to 0.69 mg/kg and As bioavailability reduced from 10.59 mg/kg to 6.86 mg/kg at 1 % IGS7 addition. The Cd and As were all transformed to more stable fractions after IGS7 addition. The acid soluble and reducible Cd fractions were transformed into oxidizable and residual Cd fractions, and the non-specifically and specifically adsorbed As fractions were transformed to amorphous iron oxide-bound As fraction. This study provides valuable references for the application of CGS to the remediation of Cd and As co-contaminated soil.

Assessment of groundwater and surface water quality in a typical mining community: application of water quality indices and hierarchical cluster analyses

The rate at which freshwater sources are being contaminated by mining operations in the South-Western part of Ghana is alarming. However, no study has quantified the degree of contamination of the freshwater in such areas, leaving a gap in the literature that requires immediate attention. This study assessed the quality of the surface and groundwater in the Tarkwa Nsuaem Municipality. Even though the physical parameters such as pH and electrical conductivity were indicative of safe freshwater, other parameters such as turbidity, total suspended solids (TSS), dissolved oxygen (DO), and heavy metals in the water sources were high; thus, confirming possible leaching, runoff, and dissolution of the hazardous substances employed in the manganese mining operations. The water quality of 82% of the water sources along the Kawere Stream was low (Classes III and IV). Therefore, the local people are at risk of contracting water-related diseases, and health problems associated with the ingestion of Fe, As, and Mn. The findings in this study are important in establishing the rate at which mining operations are reducing the quality of freshwater in developing countries, and potentially affecting human health.

Arsenic release pathway and the interaction principle among major species in vacuum sulfide reduction roasting of copper smelting flue dust

The efficient release of arsenic in copper smelting flue dust (CSFD) with complicated production conditions and composition under the premise of environmental safety is difficult for the copper smelting industry. The vacuum environment is conducive to the volatilization of low-boiling arsenic compounds, which is beneficial to the physical process and chemical reaction of increasing the volume. In the present study, combined with thermodynamic calculations, the roasting process of pyrite and CSFD mixed in proportion in vacuum was simulated. Additionally, the release process of arsenic and the interaction mechanism of the main phases were performed in detail. The addition of pyrite facilitated the decomposition of stable arsenate in CSFD into volatile arsenic oxides. The results indicated that exceeding 98% of arsenic in CSFD volatilized into the condenser, while the arsenic content in the residue was reduced to 0.32% under optimal conditions. Pyrite could reduce the oxygen potential during the chemical reaction with CSFD, reacting with sulfates in CSFD to convert into sulfides and magnetic iron oxide (Fe₃O₄) simultaneously, and Bi₂O₃ would be transformed into metallic Bi. These findings are significant for developing arsenic-containing hazardous waste treatment routes and the application of innovative technical approaches.

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.

Citrus fruit residues as alternative precursors to developing H2O and CO2 activated carbons and its application for Cu(II) adsorption

Due to its toxicity, the presence of Cu(II) ions released in aquatic environments presents a serious threat to the environment and human health. In search of sustainable and low-cost alternatives, there are citrus fruit residues, which are generated in large quantities by the juice industries and can be used to produce activated carbons. Therefore, the physical route was investigated for producing activated carbons to reuse citrus wastes. In this work, eight activated carbons were developed, varying the precursor (orange peel-OP, mandarine peel-MP, rangpur lime peel-RLP, and sweet lime peel-SLP) and the activating agent (CO₂ and H₂O) to remove Cu(II) ions of the aqueous medium. Results revealed promising activated carbons with a micro-mesoporous structure, a specific surface area of around 400 m² g^-1, and a pore volume of around 0.25 cm³ g^-1. In addition, Cu (II) adsorption was favored at pH 5.5. The kinetic study showed that the equilibrium was reached within 60 min removing about 80% of Cu(II) ions. The Sips model was the most suitable for the equilibrium data, providing maximum adsorption capacities (qmS) values of 69.69, 70.27, 88.04, 67.83 mg g^-1 for activated carbons (AC-CO₂) from OP, MP, RLP, and SLP, respectively. The thermodynamic behavior showed that the adsorption process of Cu(II) ions was spontaneous, favorable, and endothermic. It was suggested that the mechanism was controlled by surface complexation and Cu²⁺-π interaction. Desorption was possible with an HCl solution (0.5 mol L^-1). From the results obtained in this work, it is possible to infer that citrus residues could be successfully converted into efficient adsorbents to remove Cu(II) ions from aqueous solutions.

Transformation of phosphorus species during phosphoric acid-assisted pyrolysis of lignocellulose

Phosphoric acid-assisted pyrolysis (PAAP) is a pyrolysis technique with potential for the engineered and environmental application. Nevertheless, the volatilisation, immobilisation, and dissolution of phosphorus (P) species have been neglected during PAAP of lignocellulose. Therefore, we compared the transformation of P species with direct-pyrolysis and PAAP system, using multiple techniques including gas chromatography tandem mass spectrometry (GCMS) and ³¹P nuclear magnetic resonance (NMR). It was also investigated that the properties of pyrogenic and modified carbons obtained from lignocellulose pyrolysis at 200-650 °C. As the temperature increased, volatile P species evolved into gas-phase during PAAP, inhibiting the formation of the macromolecular volatile components. Compared with pyrogenic carbons, modified carbons with more aromatic structures experienced a higher degree of dehydration and cyclisation via catalytic crosslinking reaction. PAAP system facilitated more generation of persistent free radical (PFR) below 500 °C and the attenuation of PFR signals was observed at 500-650 °C, which may be associated with the sequestration and elimination of P species between carbon matrix. Notably, three configurations of C₃PO, CPO, and COP were the major combinations of P and C elements on modified carbons. Increased gaseous P and decreased soluble P were observed with elevated temperatures in PAAP system. The species proportion of immobilised P clearly demonstrated the transformation of partial P species from inorganic to organic through pyrolysis. The immobilised P could serve as a potential sustained-release source participating in P biogeochemical cycles. These findings are fundamental for the technical design of lignocellulose pyrolysis.

Simultaneous adsorption of As(III) and Pb(II) by the iron-sulfur codoped biochar composite: Competitive and synergistic effects

Simultaneous elimination of As(III) and Pb(II) from wastewater is still a great challenge. In this work, an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(III) and Pb(II). The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction. The mechanism of As(III) removal could be illustrated by surface complexation, oxidation and precipitation. In addition to precipitation and complexation, the elimination mechanism of Pb(II) also contained ion exchange and electrostatic interactions. Competitive and synergistic effects existed simultaneously in the co-contamination system. The suppression of As(III) was ascribed to competitive complexation of the two metals on Fe/S-BC, while the synergy of Pb(II) was attributed to the formation of the PbFe₂(AsO₄)₂(OH)₂. Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(III) and Pb(II), regardless of pH dependency and interference by various coexisting ions. The maximum adsorption capacities of the Fe/S-BC for As(III) and Pb(II) were 91.2 mg/g and 631.7 mg/g, respectively. Fe/S-BC could be treated as a novel candidate for the elimination of As(III)-Pb(II) combined pollution.

An assessment of the efficacy of biochar and zero-valent iron nanoparticles in reducing lead toxicity in wheat (Triticum aestivum L.)

Soil heavy metal contamination is increasing rapidly due to increased anthropogenic activities. Lead (Pb) is a well-known human carcinogen causing toxic effects on humans and the environment. Its accumulation in food crops is a serious hazard to food security. Developing environment-friendly and cost-efficient techniques is necessary for Pb immobilization in the soil. A pot experiment was executed to determine the role of biochar (BC), zero-valent iron nanoparticles (n-ZVI), and zero-valent iron nanoparticles biochar composite (n-ZVI-BC) in controlling the Pb mobility and bioaccumulation in wheat (Triticum aestivum L.). The results showed that BC and n-ZVI significantly enhanced the wheat growth by increasing their photosynthetic and enzymatic activities. Among all the applied treatments, the maximum significant (p ≤ 0.05) improvement in wheat biomass was with the n-ZVI-BC application (T3). Compared to the control, the biomass of wheat roots, shoots & grains increased by 92.5, 58.8, and 49.1%, respectively. Moreover, the soil addition of T3 amendment minimized the Pb distribution in wheat roots, shoots, and grains by 33.8, 26.8, and 16.2%, respectively. The outcomes of this experiment showed that in comparison to control treatment plants, soil amendment with n-ZVI-BC (T3) increased the catalase (CAT), superoxide dismutase (SOD) activity by 49.8 and 31.1%, respectively, ultimately declining electrolyte leakage (EL), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content in wheat by 38.7, 33.3, and 38%respectively. In addition, applied amendments declined the Pb mobility in the soil by increasing the residual Pb fractions. Soil amendment with n-ZVI-BC also increased the soil catalase (CAT), urease (UR), and acid phosphatase (ACP) activities by 68, 59, and 74%, respectively. Our research results provided valuable insight for the remediation of Pb toxicity in wheat. Hence, we can infer from our findings that n-ZVI-BC can be considered a propitious, environment friendly and affordable technique for mitigating Pb toxicity in wheat crop and reclamation of Pb polluted soils.

Enhanced elimination of Cr(VI) from aqueous media by polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero valent iron: Performance and mechanism

A novel polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero-valent iron (S-nZVI@PBC) was developed to enhance Cr(VI) removal from aqueous media. The characteristics of morphology, chemical composition, and functional groups of S-nZVI@PBC, as well as its kinetics and mechanism for Cr(VI) removal were explored. Characterization verified S-nZVI was successfully loaded onto PEI modified biochar. The adsorption process was well represented pseudo-second-order model (R² = 0.990) and Langmuir isotherm model (R² = 0.962), indicating it was a monolayer chemical adsorption process. The Cr(VI) removal was affected by pH and achieved the maximum when pH = 3.0, which may be ascribed to the better corrosion of nZVI and release of Fe(II) from the S-nZVI@PBC in acidic condition. The primary mechanisms were adsorption, reduction, and co-precipitation. S-nZVI@PBC exhibited higher stability and reusability than nZVI, which makes it more promising in environmental application. Overall, S-nZVI@PBC is of great potential for treating Cr(VI)-containing wastewater.

Facile encapsulation of nano zero-valent iron with calcium carbonate: synthesis, characterization and application for iron remediation

In this study, CaCO3 was used as a modifier for nano zero-valent iron (nZVI) surface to prevent rapid aggregation and effectively utilized for iron remediation from aqueous solution. Surface chemistry and morphology of CaCO3 encapsulated nZVI (CaCO3-nZVI) before and after treatment of contaminant iron solution were characterized by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The mechanisms of surface modification as well as iron remediation were well depicted with the help of these characterisation tools. Iron removal efficacy of 96.4% was achieved with 0.25 g/L adsorbent dose for an influent iron of 0.5 mg/L at pH 10 after a 3 h treatment process. When the influent concentration was increased to 10 mg/L, the removal capacity decreased to 92.1%. The study demonstrates that CaCO3 and nZVI in the encapsulated nanoparticle have a significant synergistic effect. The pseudo-second- order reaction kinetics and Freundlich isotherm model correctly portrayed the experimental data for iron removal by CaCO3-nZVI. The CaCO3-nZVI is a viable option for iron removal from various aqueous media due to its facile preparation, high iron removal capability, and reusability.

Immobilized Nanomaterials for Environmental Applications

Nanomaterials (NMs) have been extensively used in several environmental applications; however, their widespread dissemination at full scale is hindered by difficulties keeping them active in engineered systems. Thus, several strategies to immobilize NMs for their environmental utilization have been established and are described in the present review, emphasizing their role in the production of renewable energies, the removal of priority pollutants, as well as greenhouse gases, from industrial streams, by both biological and physicochemical processes. The challenges to optimize the application of immobilized NMs and the relevant research topics to consider in future research are also presented to encourage the scientific community to respond to current needs.

Functionalized biochars: Synthesis, characterization, and applications for removing trace elements from water

Biochar (BC) has been recognized as an effective adsorbent to remove trace elements (TEs) from water. However, low surface functionality and small pore size can limit the adsorption ability of pristine biochar. These limitations can be addressed by using functionalized biochars which are developed by physical, chemical, or biological activation of biochar to improve their physico-chemical properties and adsorption efficiency. Despite the large amount of research concerning functionalized biochars in recent decades, to our knowledge, no comprehensive review of this topic has been published. This review focuses solely on the synthesis, characterization, and applications of functionalized/engineered biochars for removing TEs from water. Firstly, we evaluate the synthesis of functionalized biochars by physical, chemical, and biological strategies that yield the desired properties in the final product. The following section describes the characterization of functionalized biochars using various techniques (SEM, TEM, EDS, XRD, XANES/NEXAFS, XPS, FTIR, and Raman spectroscopy). Afterward, the role of functionalized biochars in the adsorption of different TEs from water/wastewater is critically evaluated with an emphasis on the factors affecting sorption efficiency, sorption mechanisms, fate of sorbed TEs from contaminated environments and associated challenges. Finally, we specifically scrutinized the future recommendations and research directions for the application of functionalized biochar. This review serves as a comprehensive resource for the use of functionalized biochar as an emerging environmental material capable of removing TEs from contaminated water/wastewater.

Co-Removal Effect and Mechanism of Cr(VI) and Cd(II) by Biochar-Supported Sulfide-Modified Nanoscale Zero-Valent Iron in a Binary System

This study aimed to explore the co-removal effect and mechanism of Cr(VI) and Cd(II) with an optimized synthetic material. The toxicity and accumulation characteristics of Cr(VI) and Cd(II) encountered in wastewater treatment areas present significant challenges. In this work, a rational assembly of sulfide-modified nanoscale zero-valent iron (SnZVI) was introduced into a biochar (BC), and a Cr(VI)–Cd(II) binary system adsorbent with high efficiency was synthesized. When the preparation temperature of the BC was 600 °C, the molar ratio of S/Fe was 0.3, the mass ratio of BC/SnZVI was 1, and the best adsorption capacities of BC-SnZVI for Cr(VI) and Cd(II) in the binary system were 58.87 mg/g and 32.55 mg/g, respectively. In addition, the adsorption mechanism of BC-SnZVI on the Cr(VI)-Cd(II) binary system was revealed in depth by co-removal experiments, indicating that the coexistence of Cd(II) could promote the removal of Cr(VI) by 9.20%, while the coexistence of Cr(VI) could inhibit the removal of Cd(II) by 43.47%. This work provides a new pathway for the adsorption of Cr(VI) and Cd(II) in binary systems, suggesting that BC-SnZVI shows great potential for the co-removal of Cr(VI) and Cd(II) in wastewater.

Enhanced Cr(VI) stabilization in soil by chitosan/bentonite composites

In this study, chitosan/bentonite composites (CSBT) was synthesized and applied to the immobilization of chromium in the soil. The influence of passivating agents on various forms of chromium was investigated by batch experiment. The results showed that CSBT could reduce the content of exchangeable form and oxidizable form, while increase the content of residual form of chromium. The addition of 0.2 g·kg^-1 CSBT had the best effect, with the concentration of exchangeable, reducible and oxidizable form decreased by 46.74%, 8.15%, and 14.46%, respectively. During the experiment time, the passivation effect increased rapidly within 14 days, and the content of residual form in the total Cr increased from 0.76% to 14.23%, the equilibrium was reached at the 28th day and was basically maintained in the subsequent period. CSBT had little impact on soil pH, and soil pH maintained constant during the experiment period. The amino, carboxyl and hydroxyl groups of CSBT promoted the conversion of available chromium to residual state in soil, and reduced the bioavailability of chromium in soil.

Mechanism-Enhanced Active Attapulgite-Supported Nanoscale Zero-Valent Iron for Efficient Removal of Pb2+ from Aqueous Solution

In this study, attapulgite-supported nano zero-valent iron (nZVI@ATP) was synthesized by a liquid-phase reduction method using active attapulgite (ATP) as raw material, and used for Pb2+ remediation in aqueous solution. To understand the mechanism of Pb2+ removal, various techniques were used to characterize nZVI@ATP. The results showed that spherical nZVI particles were uniformly dispersed on the surface of ATP, and the agglomeration of nZVI particles was significantly weakened. The adsorption performance of nZVI@ATP for Pb2+ was greatly improved compared with that of ATP ore, in which the Fe/ATP mass ratio of 1:2 was the best loading ratio. Under the conditions of a temperature of 25 °C and a pH of 5.00, the initial concentration of Pb2+ was 700 mg/L, and the Pb2+ removal rate of nZVI@ATP was 84.47%. The adsorption of nZVI@ATP to Pb2+ was mainly a spontaneous endothermic reaction of heterogeneous surfaces, and the adsorption rate of nZVI@ATP to Pb2+ was proportional to pH in the range of 2–5.5. The presence of Na+, Mg2+, and Ca2+ can inhibit the removal of Pb2+, and Ca2+ has the strongest inhibition effect on the removal of Pb2+. The removal mechanism of Pb2+ by nZVI@ATP obtained from SEM-EDS, BET, XRD, FTIR and XPS included reduction, precipitation, and the formation of complexes.

Abrogating the inhibitory effects of volatile fatty acids and ammonia in overloaded food waste anaerobic digesters via the supplementation of nano-zero valent iron modified biochar

The effects of different recovery strategies on inhibited anaerobic digestion (AD) of food waste (FW) was examined in this study, with the finding that dosing pine woodchip biochar could reverse the effect of volatile fatty acids (VFA) inhibition (mainly propionic acid) and yielded 105.55% more methane than the control. The addition of nano-zerovalent iron (nZVI) promoted the generation of VFA while causing a slight inhibition of the methanogens initially. In due time, the nZVI digester was able to recover and eventually produced 192.22% more methane compared to the control. Finally, nZVI-modified biochar was proved to be able to avoid the inhibitory effects brought about by the nanoparticles. The results indicated reduced dosage requirements as compared to using pristine pine woodchip biochar and accumulated 204.84% more methane than the control. The introduction of nZVI-biochar also promoted the growth of Methanosarcina species methanogens, which can perform direct-interspecies electron transfer. While all the recovery strategies using the additives were feasible, the results suggested that the use of modified biochar holds great potential as a significantly lower amount of amendment is required for the recovery of the inhibited AD system.

Biochar-supported nanoscale zero-valent iron can simultaneously decrease cadmium and arsenic uptake by rice grains in co-contaminated soil

Cadmium (Cd) and Arsenic (As) in rice grains are a primary exposure source for human beings. However, the simultaneous stabilization of Cd and As in soil becomes difficult due to the opposite properties of those. In this study, we investigated the simultaneous effects of biochar-supported nanoscale zero-valent iron (nZVI-BC) and water management on the decrease of Cd and As bioaccumulation in rice grain. Compared to the control, 0.25-1.00% nZVI-BC coupled with alternate wetting and drying (AWD) management simultaneously decreased the bioaccumulation of Cd and As in rice grains by 15.85-69.16% and 23.06-59.45%, respectively. The cancer risk associated with rice consumption effectively reduced by 15.60-52.41% after the application of nZVI-BC, and the lowest cancer risk was detected in 1.00% nZVI-BC under AWD management. Furthermore, rice cultivated under AWD management had a lower total cancer risk than that cultivated under continuous flooded (CF) management with the same amendment of type and dose. The reduction of soil Cd and As availability and the formation of iron plaque dominated the decrease of Cd and As uptake by rice grains. The elevated soil pH was responsible for Cd adsorption, and the dominant mechanism for As immobilization was the formation of complexes. The iron plaque was double-edged, promoting and inhibiting Cd uptake by rice, wherein the inhibition was predominant under aerobic conditions. In addition, iron plaque was a barrier to preventing the As accumulation by rice, a larger amount of As was immobilized on the iron plaque with nZVI-BC treatment. This study sheds new insights on the simultaneous remediation of Cd and As co-contaminated paddy fields.

Recent advances of carbon-based nano zero valent iron for heavy metals remediation in soil and water: A critical review

Heavy metal pollution in soil and water has presented a new challenge for the environmental remediation technology. Nano zero valent iron (nZVI) has excellent adsorbent properties for heavy metals, and thus, exhibits great potential in environmental remediation. Used as supporting materials for nZVI, carbon-based materials, such as activated carbon (AC), biochar (BC), carbon nanotubes (CNTs), and graphene (GNs) with aromatic rings formed by carbon atoms as the skeleton, have a large specific surface area and porous structure. This paper provides a comprehensive review on the advancement of carbon-based nano zero valent iron (C-nZVI) particles for heavy metal remediation in soil and water. First, different types of carbon-based materials and their combination with nZVI, as well as the synthesis methods and common characterization techniques of C-nZVI, are reviewed. Second, the mechanisms for the interactions between contaminants and C-nZVI, including adsorption, reduction, and oxidation reactions are detailed. Third, the environmental factors affecting the remediation efficiency, such as pH, coexisting constituents, oxygen, contact time, and temperature, are highlighted. Finally, perspectives on the challenges for utilization of C-nZVI in the actual contaminated soil and water and on the long-term efficacy and safety evaluation of C-nZVI have been proposed for further development.

Remediation of emerging metal pollutants using environment friendly biochar- Review on applications and mechanism

Bioremediation of heavy metals has become a major environmental concern due to their bio resistant nature and tendency to accumulate. Application of various technologies, involving physical and chemical working principles are applied and passive uptake using sorption involving eco-friendly substrates gained significant attention. Biochar, a cheaper and efficient material, offers good potential due to the greater ease of production, treatment and disposal. This review focuses on the effective application of biochar to treat water contaminated by three specific heavy metals: chromium, lead and arsenic. The on-field applications like soil amendment, industrial wastewater treatment and groundwater treatment using biochar are highlighted. The review article describes the feedstock available for biochar production, various production processes and the importance of optimum conditions like pyrolysis temperature, rate and retention time for various feedstocks reported in literature. The energy requirement of the production process can be supplied by its own energy output. Various modifications that are suitable for the biochar from distinct feedstocks are also discussed. The removal performance of biochar at different working conditions like pH, initial concentration of pollutant and adsorbent dose are consolidated. The highest removal efficiencies reported were by coconut shell biochar (Cr - 99.9%), canola straw biochar (Pb - 100%) and perilla leaf biochar (As - 100%). The adsorption mechanism is explained with reference to kinetics, isotherms, and molecular dynamics. Adsorption mechanism of most of the biochars was found to fit either Freundlich or Langmuir isotherm.

Removal mechanism of 17β-estradiol by carbonized green synthesis of Fe/Ni nanoparticles

Even a small concentration of estrogen released into the environment can cause great damage to the surrounding ecosystem, with potential teratogenic and carcinogenic hazards to many organisms. In this study, carbonized green synthesized Fe/Ni NPs, with a maximum adsorption capacity of 44.32 mg g^-1 coupled with over 98.3% removal efficiency, were used to remove 17β-estradiol (E2) from water. Adsorption best conformed to pseudo-second-order kinetics (R² = 0.998-0.999) and the Freundlich model (R² = 0.990-0.997). SEM images reveal that the carbonized material had increased specific surface area and pores. Zeta Potential, FTIR and XPS spectra confirmed that carbonized material was negatively charged and contained functional groups with a high affinity for E2. Liquid chromatography during removal of E2 suggested no new substances were generated. Therefore, the synergistic effect of carbonized-Fe/Ni NPs surface functional groups is a key issue, including dehydration bonds, hydrogen bonds, and the accumulation of Π and Π. In practice the application of carbonized-Fe/Ni NPs demonstrated their ability to remove 51.8% and 48.7% of E2 from domestic sewage and livestock wastewater, respectively. This work provides a strong basis for the practical removal of E2 using carbonized-Fe/Ni NPs material.

Nanotechnology in the Restoration of Polluted Soil

The advancements in nanoparticles (NPs) may be lighting the sustainable and eco-friendly path to accelerate the removal of toxic compounds from contaminated soils. Many efforts have been made to increase the efficiency of phytoremediation, such as the inclusion of chemical additives, the application of rhizobacteria, genetic engineering, etc. In this context, the integration of nanotechnology with bioremediation has introduced new dimensions for revamping the remediation methods. Hence, advanced remediation approaches combine nanotechnological and biological remediation methods in which the nanoscale process regulation supports the adsorption and deterioration of pollutants. Nanoparticles absorb/adsorb a large variety of contaminants and also catalyze reactions by lowering the energy required to break them down, owing to their unique surface properties. As a result, this remediation process reduces the accumulation of pollutants while limiting their spread from one medium to another. Therefore, this review article deals with all possibilities for the application of NPs for the remediation of contaminated soils and associated environmental concerns.

Efficiency assessment of ZVI-based media as fillers in permeable reactive barrier for multiple heavy metal-contaminated groundwater remediation

Four zero valent iron-based composites were prepared and applied as the reactive media of permeable reactive barriers. Batch tests and continuous-flow column experiments were conducted to assess the long-term performance of these composites for possible utilization as fillers for PRB. The experimental results of the batch tests revealed that in single-metal systems, the removal efficiency of Cu(Ⅱ), Co(Ⅱ), Cr(Ⅵ) and As(Ⅲ) could reach 98% at equilibrium. Equilibrium data showed that composites displayed different selectivity values in binary and quaternary-component systems. For the continuous tests, column filled with chitosan-zero valent iron-based composites, exhibited optimal removal efficiency and achieved average removal values of 98.84%, 88.28%, 95.65% and 87.10% for Cu(Ⅱ), Co(Ⅱ), Cr(Ⅵ) and As(Ⅲ) during the whole 30-day operation, respectively. Dynamic removal improvement of multiple metals was observed with further assembly media, with average removal of 99.11%, 90.05% and 87.34% for Cu(Ⅱ), Co(Ⅱ) and As(Ⅲ), respectively. Combined with superficial characteristic analysis, the functional groups distributed on the surface of composites played a key role in metal sorption. Moreover, the adsorbed Cu(Ⅱ), Co(Ⅱ) and Cr(Ⅵ) gradually transferred to the mobile phase when the operational periods were prolonged, while As(Ⅲ) became more stable.

Optimizing magnetic functionalization conditions for efficient preparation of magnetic biochar and adsorption of Pb(II) from aqueous solution

Recoverable magnetic biochar has great potential for treating wastewater contaminants such as Pb(II). However, whether magnetic modification could enhance metal adsorption efficiency is currently contradictory in the literature mainly due to the differences in selecting various magnetic functionalization conditions. Considering this gap in knowledge, the effects of magnetic functionalization method (impregnation and precipitation), concentration of precursor iron solution (0.01-1 M), and pyrolysis temperature (300-700 °C) on the characteristics and Pb(II) adsorption capacity of biochar were systematically investigated in this paper. Results indicated that Fe₃O₄ was the main product for magnetic biochars synthesized using the impregnation (denoted as FWFe(3)) and precipitation methods (denoted as FWFe(2)). Magnetic functionalization resulted in remarkably increased pH and more negative zeta potential for FWFe(2) samples, whereas FWFe(3) samples showed the opposite trends. The adsorption of Pb(II) on different biochars fitted the pseudo-second order model and the Langmuir model. The maximum adsorption capacity was 817.64 mg/g for FWFe(2)1M700C (precipitation by 1 M of Fe(II)/Fe(III), pyrolysis at 700 °C), outperforming FWFe(3) and pristine biochar samples by around 5-13 times. Mechanism study indicated that the adsorption mainly involved electrostatic attraction, ion exchange, co-precipitation, and complexation. Pb(II) adsorption capacity was strongly dependent on the alkali pH of biochar. However, this efficiency was less affected by biochar surface area and its morphology. The higher pH of FWFe(2) samples not only led to an increased surface charge for stronger electrostatic attraction and ion exchange but also favored the formation of co-precipitates. By contrast, FWFe(3) samples showed a decreased adsorption capacity for Pb(II) with increased concentration of embedded iron. Overall, magnetic biochar, prepared using precipitation followed by high-temperature pyrolysis (such as, FWFe(2)1M700C), can be a promising adsorbent for Pb(II) adsorption from wastewater.

A versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar for simultaneous removal of methyl orange and heavy metals from complex wastewater

At present, the simultaneous removal of organic dyes and heavy metals in complex wastewater has raised considerable concern, owing to their striking differences in physicochemical properties. Adsorption, as one of the few removal methods, has attracted extensive attention and gained popularity. Herein, a versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar adsorbent (ECMBB) was synthesized for coinstantaneous adsorption of methyl orange (MO) and heavy metals (Cd(II) and Zn(II)). In this case, the as-synthesized ECMBB composites inherited favorable anionic MO removal performance from bamboo biochar (BB) obtained at 700 °C through electrostatic attraction, hydrogen bonding and π-π interaction, also enhanced the binding of cationic metals by introducing amino groups of chitosan and carboxyl groups of EDTA. In the unitary system, the removal of MO, Cd(II) and Zn(II) by three as-prepared adsorbents can be well illuminated by pseudo-second-order kinetic model and Langmuir isotherm theory. The saturated capture amounts of ECMBB at 25 °C are 305.4 mg g^-1 for MO, 63.2 mg g^-1 for Cd(II) and 50.8 mg g^-1 for Zn(II), which, under the same conditions, are 1.3, 2.6 and 2.5 times those of chitosan-modified magnetic bamboo biochar (CMBB) and 1.9, 6.1 and 5.4 times those of magnetic bamboo biochar (MBB), respectively. Remarkably, in MO-metal binary system, coexisting MO visibly enhanced the adsorption of Cd(II) and Zn(II), while coexisting heavy metals had no significant impact on MO adsorption. Furthermore, ECMBB exhibited no significant loss in adsorption efficiency even after eight adsorption-desorption experiments. This study lays the foundation for fabricating desired integrative biochar adsorbents in the simultaneous purification of organic and metallic pollutants from complex wastewater.

A state-of-the-art review on modeling the biochar effect: Guidelines for beginners

Biochar has been widely advocated due to its special properties and sustainability for agriculture soil amendment. The influencing mechanism of biochar on soil properties is a key aspect of quantifying and predicting its benefits and trade-offs. The contribution of biochar to both environmental and agricultural benefits has been deeply discussed and extensively reviewed, but few reviews have focused on modeling biochar effects. An overview of recent advances in biochar modeling is illustrated and approaches classified in this paper. Applications of a machine learning model, a deterministic model, and a numerical model to biochar are categorized and summarized. A discussion of the advantages and disadvantages of each model and a comparison among them are also provided. Finally, this paper gives many suggestions on narrowing the knowledge gap to advance biochar modeling. Further study of biochar modeling in management planning and design and application of the model results in agricultural systems will help accelerate the expansion of biochar's application scale and encourage the efficient utilization of waste in agricultural systems.

Adsorption of metal on pineapple leaf biochar: Key affecting factors, mechanism identification, and regeneration evaluation

Although tremendous works have been done on metal adsorption via biochar, mechanisms responsible for metal adsorption remain uncertain. This is the first work that provides direct evidence on the identification of Ni(II), Zn(II), and Cu(II) adsorption mechanisms on pineapple leaf biochar (PLB) using surface characteristics analyses, including X-ray photoelectron spectroscope (XPS), Fourier transform infrared spectroscope (FTIR), and scanning electron microscope with energy-dispersive X-ray spectroscope (SEM-EDS). From Langmuir isotherm fitting, the maximum adsorption capacity of PLB for Ni(II), Zn(II), and Cu(II) are 44.88, 46.00, and 53.14 mg g^-1, respectively, surpassing all biochars reported in the literature. Findings of surface characterization techniques coupled with cation released during adsorption, cation exchange, and surface complexation mechanisms were proposed. PLB is reusable and remains sufficient adsorption capacity even six consecutive cycles via pressure cooker regeneration. With high regenerability and ultrahigh adsorption capacity, PLB defines itself as a promising adsorbent for future applications in metal-laden wastewater.

Roadmap of Effects of Biowaste-Synthesized Carbon Nanomaterials on Carbon Nano-Reinforced Composites

Sustainable growth can be achieved by recycling waste material into useful resources without affecting the natural ecosystem. Among all nanomaterials, carbon nanomaterials from biowaste are used for various applications. The pyrolysis process is one of the eco-friendly ways for synthesizing such carbon nanomaterials. Recently, polymer nanocomposites (PNCs) filled with biowaste-based carbon nanomaterials attracted a lot of attention due to their enhanced mechanical properties. A variety of polymers, such as thermoplastics, thermosetting polymers, elastomers, and their blends, can be used in the formation of composite materials. This review summarizes the synthesis of carbon nanomaterials, polymer nanocomposites, and mechanical properties of PNCs. The review also focuses on various biowaste-based precursors, their nanoproperties, and turning them into proper composites. PNCs show improved mechanical properties by varying the loading percentages of carbon nanomaterials, which are vital for many defence- and aerospace-related industries. Different synthesis processes are used to achieve enhanced ultimate tensile strength and modulus. The present review summarizes the last 5 years’ work in detail on these PNCs and their applications.

Preparation of binder-less activated char briquettes from pyrolysis of sewage sludge for liquid-phase adsorption of methylene blue

Binder-less activated char briquettes from sewage sludge were prepared and used for the liquid-phase adsorption of methylene blue. The properties of sludge char briquettes prepared under the different initial sludge moisture content, compression pressure, and heating rate were systematically investigated through the tests of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), surface and mechanical properties, burn-off rates, methylene blue adsorption kinetics and isotherms. All of the prepared briquettes presented hierarchical structures and microporous/mesoporous characteristics, and the increase of initial sludge moisture content from 10 to 30 wt% resulted in a great increase of surface area (S_BET), total pore volume (V_T), apparent density, and a slight decrease of mechanical performance. The decrease of compression pressure markedly enhanced the equilibrium adsorption capacity (q_{e, exp}), owing to the decreased diffusion resistance and blockage of diffusion pathways inside briquettes. In consideration of the mechanical performance and adsorption capacity, the optimum preparation condition was obtained at the initial moisture content of 30 wt%, compression pressure of 25 MPa, and heating rate of 10 °C/min, in which the axial compressive strength (ACS) and q_{e, exp} of the prepared briquettes were as high as 22.2 ± 3.1 kg/m² and 316.9 mg/g. The results also showed that the equilibrium adsorption data fit well into the pseudo-first order model system, and the adsorption isotherms followed the Langmuir isotherm model, suggesting that the adsorption process was attributed to physical adsorption, and was inclined to happen on the adsorption sites with the same energy level. Finally, the thermal regeneration tests demonstrated that the binder-less briquette had a good regeneration performance and was worthy of reusing for industrial applications.