Superefficient Removal of Heavy Metals from Wastewater by Mg-Loaded Biochars: Adsorption Characteristics and Removal Mechanisms

Removal of Cu(II) and Cr(VI) from electroplating wastewater by magnetic Fe3O4@SiO2-UiO-66-EDTA: Adsorption behavior and mechanism

The heavy metals discharged from electroplating wastewater, represented as copper and chromium ions, is harmful to aquatic lives and human beings, and will break the ecological balance. In this work, magnetic hybrid porous structure adsorbent of Fe3O4@SiO2-UiO-66-EDTA is prepared for recycling copper and chromium ions. The adsorbent exhibits a maximum adsorption capacity of 212.10 mg/g for Cu(II) and 118.10 mg/g for Cr(VI). Notably, it shows excellent regenerability of 80.89% after 10 cycles. The adsorption of Cu(II) and Cr(VI) on Fe3O4@SiO2-UiO-66-EDTA follows the pseudo-second-order model, where chemical adsorption is dominant and it occurs spontaneously and exothermally. Based on XRD, FTIR, XPS, and DFT calculations, the adsorption mechanisms are driven by electrostatic attraction, chelation, and redox reactions. This work provides a novel and promising strategy for designing highly efficient adsorbents, paving the way for more effective treatments of electroplating wastewater contaminated with Cu(II) and Cr(VI).

Environmental colloid behaviors of humic acid - Cadmium nanoparticles in aquatic environments

Humic acid (HA), a principal constituent of natural organic matter (NOM), manifests ubiquitously across diverse ecosystems and can significantly influence the environmental behaviors of Cd(II) in aquatic systems. Previous studies on NOM-Cd(II) interactions have primarily focused on the immobilization of Cd(II) solids, but little is known about the colloidal stability of organically complexed Cd(II) particles in the environment. In this study, we investigated the formation of HA-Cd(II) colloids and quantified their aggregation, stability, and transport behaviors in a saturated porous media representative of typical subsurface conditions. Results from batch experiments indicated that the relative quantity of HA-Cd(II) colloids increased with increasing C/Cd molar ratio and that the carboxyl functional groups of HA dominated the stability of HA-Cd(II) colloids. The results of correlation analysis between particle size, critical aggregation concentration (CCC), and zeta potential indicated that both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions contributed to the enhanced colloidal stability of HA-Cd(II) colloids. Column results further confirmed that the stable HA-Cd(II) colloid can transport fast in a saturated media composed of clean sand. Together, this study provides new knowledge of the colloidal behaviors of NOM-Cd(II) nanoparticles, which is important for better understanding the ultimate cycling of Cd(II) in aquatic systems.

Natural Degradation Behavior of Poly(lactic acid) Nanocomposite Films and the Adsorption Behavior of Degraded Products on Cu(II)

In this study, the degradation behavior of poly(lactic acid) nanocomposite films (PLA/Hec-g@PS) under extreme natural environments was investigated, and the degraded PLA based films were applied to adsorb Cu(II). During the early and midstages of degradation, the surface roughness and crack propagation rate of PLA/Hec-g@PS films were significantly lower than those of PLA films. This could be due to the fact that Hec-g@PS enhanced the interaction forces between C-O-C + CH3 and C═O in the PLA chains, thereby mitigating the degradation of PLA. Neural network predictions indicated that the molecular weight of PLA films decreased to 30% after 1344 days, whereas PLA/Hec-g@PS films reached the same reduction in 1451 days, extending the lifespan of PLA by 1.08 times. The environmental impact of PLA/Hec-g@PS was further assessed by their adsorption behavior toward Cu(II). It was found that PLA films adsorbed 244.51 μg/g of Cu(II), while PLA/Hec-g@PS films adsorbed 372.63 μg/g of Cu(II). The isotherm adsorption model showed that the maximum adsorption capacities (qm) of PLA and PLA/Hec-g@PS were 326.60 μg/g and 441.51 μg/g, respectively. This improvement offers PLA based films new possibilities for applications in wastewater treatment and soil remediation.

Exploring nanomaterial-modified biochar for environmental remediation applications

Environmental pollution, particularly from heavy metals and toxic elements, poses a significant threat to both human health and ecological systems. While various remediation technologies exist, there is an urgent need for cost-effective and sustainable solutions. Biochar, a carbon-rich product derived from the pyrolysis of organic matter, has emerged as a promising material for environmental remediation. However, its pristine form has limitations, such as low adsorption capacities, a relatively narrow range of pH adaptability which can limit its effectiveness in diverse environmental conditions, and a tendency to lose adsorption capacity rapidly in the presence of competing ions or organic matters. This review aims to explore the burgeoning field of nanomaterial-modified biochar, which seeks to overcome the limitations of pristine biochar. By incorporating nanomaterials, the adsorptive and reactive properties of biochar can be significantly enhanced. Such modifications, especially biochar supported with metal nanoparticles (biochar-MNPs), have shown promise in various applications, including the removal of heavy metals, organic contaminants, and other inorganic pollutants from aqueous environments, soil, and air. This review provides a comprehensive overview of the synthesis techniques, characterization methods, and applications of biochar-MNPs, as well as discusses their underlying mechanisms for contaminant removal. It also offers insights into the advantages and challenges of using nanomaterial-modified biochar for environmental remediation and suggests directions for future research.

Mechanism Study on the Immobilization of Cu2+/Pb2+ in Aqueous Phase by Mineral Co-Milling-Modified Biochar

A large number of studies have shown that the modification of biochar can greatly improve its adsorption capacity. This study adopts a one-step ball milling technology without solvent medium, using sawdust biochar (600 °C) and attapulgite/diatomaceous earth to prepare MABC10%/MDBC10% (mass ratio: 10% attapulgite/diatomite +90% biochar coabrasive). Characterization experiments show that attapulgite/diatomite was successfully loaded on biochar and has more C/O functional groups and wider adsorption pore sizes. Adsorption kinetics and isotherm experiments show that the adsorption process of MABC10% and MDBC10% on Cu2+/Pb2+ was mainly multilayer chemical adsorption. The adsorption capacities of MABC10% and MDBC10% for Cu2+ were 40.85 and 65.20 mg·L-1, respectively. The adsorption amounts of Pb2+ were 82.63 and 71.32 mg·L-1, respectively. The particle diffusion model shows that the adsorption process was controlled by both the surface adsorption rate limitation and boundary layer diffusion. The higher acidity in the solution will cause part of the negative charges on the surface of attapulgite/diatomite to be neutralized, thereby hindering its adsorption of Cu2+/Pb2+. The presence of coexisting ions did not significantly affect the adsorption performance. Mechanistic studies have shown that pore diffusion, active sites provided by C/O functional groups, electrostatic interactions, and cation exchange are the main mechanisms of MABC10% adsorption of Cu2+/Pb2+. In summary, MABC10% has a significant adsorption synergistic effect compared to MBC. It was an economical and effective adsorbent, and the higher the pH value of the wastewater, the more significant the adsorption effect.

Adsorption of Cd2+ by Lactobacillus plantarum Immobilized on Distiller's Grains Biochar: Mechanism and Action

Immobilized microbial technology has recently emerged as a prominent research focus for the remediation of heavy metal pollution because of its superior treatment efficiency, ease of operation, environmental friendliness, and cost-effectiveness. This study investigated the adsorption characteristics and mechanisms of Cd2+ solutions by Lactobacillus plantarum adsorbed immobilized on distiller's grains biochar (XIM) and Lactobacillus plantarum-encapsulated immobilized on distiller's grains biochar (BIM). The findings reveal that the maximum adsorption capacity and efficiency were achieved at a pH solution of 6.0. Specifically, at an adsorption equilibrium concentration of cadmium at 60 mg/L, XIM and BIM had adsorption capacities of 8.40 ± 0.30 mg/g and 12.23 ± 0.05 mg/g, respectively. BIM demonstrated noticeably greater adsorption capacities than XIM at various cadmium solution concentrations. A combination of isothermal adsorption modeling, kinetic modeling, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffractometer (XRD), and Fourier-transform infrared spectroscopy (FTIR) analyses showed that cadmium adsorption by XIM primarily involved physical adsorption and pore retention. In contrast, the adsorption mechanism of BIM was mainly attributed to the formation of Cd(CN)2 crystals.

Mechanisms for synergistically enhancing cadmium remediation performance of biochar: Silicon activation and functional group effects

This work proposes an advanced biochar material (β-CD@SiBC) for controllable transformation of specific silicon (Si) forms through endogenous Si activation and functional group introduction for efficient cadmium (Cd) immobilization and removal. The maximum adsorption capacity of β-CD@SiBC for Cd(II) reached 137.6 mg g-1 with a remarkable removal efficiency of 99 % for 200 mg L-1Cd(II). Moreover, the developed β-CD@SiBC flow column exhibited excellent performance at the environmental Cd concentration, with the final concentration meeting the environmental standard for surface water quality (0.05 mg L-1). The remediation mechanism of β-CD@SiBC could be mainly attributed to mineral precipitation and ion exchange, which accounted for 42 % and 29 % of the remediation effect, respectively, while functional group introduction enhanced its binding stability with Cd. Overall, this work proposes the role and principle of transformation of Si forms within biochar, providing new strategies for better utilizing endogenous components in biomass.

Recent Progress on the Adsorption of Heavy Metal Ions Pb(II) and Cu(II) from Wastewater

With the processes of industrialization and urbanization, heavy metal ion pollution has become a thorny problem in water systems. Among the various technologies developed for the removal of heavy metal ions, the adsorption method is widely studied by researchers and various nanomaterials with good adsorption performances have been prepared during the past decades. In this paper, a variety of novel nanomaterials with excellent adsorption performances for Pb(II) and Cu(II) reported in recent years are reviewed, such as carbon-based materials, clay mineral materials, zero-valent iron and their derivatives, MOFs, nanocomposites, etc. The novel nanomaterials with extremely high adsorption capacity, selectivity and particular nanostructures are summarized and introduced, along with their advantages and disadvantages. And, some future research priorities for the treatment of wastewater are also prospected.

Biochar as a partner of plants and beneficial microorganisms to assist in-situ bioremediation of heavy metal contaminated soil

Synergistic remediation of heavy metal (HM) contaminated soil using beneficial microorganisms (BM) and plants is a common and effective in situ bioremediation method. However, the shortcomings of this approach are the low colonisation of BM under high levels of heavy metal stress (HMS) and the poor state of plant growth. Previous studies have overlooked the potential of biochar to mitigate the above problems and aid in-situ remediation. Therefore, this paper describes the characteristics and physicochemical properties of biochar. It is proposed that biochar enhances plant resistance to HMS and aids in situ bioremediation by increasing colonisation of BM and HM stability. On this basis, the paper focuses on the following possible mechanisms: specific biochar-derived organic matter regulates the transport of HMs in plants and promotes mycorrhizal colonisation via the abscisic acid signalling pathway and the karrikin signalling pathway; promotes the growth-promoting pathway of indole-3-acetic acid and increases expression of the nodule-initiating gene NIN; improvement of soil HM stability by ion exchange, electrostatic adsorption, redox and complex precipitation mechanisms. And this paper summarizes guidelines on how to use biochar-assisted remediation based on current research for reference. Finally, the paper identifies research gaps in biochar in the direction of promoting beneficial microbial symbiotic mechanisms, recognition and function of organic molecules, and factors affecting practical applications.

Nanoscale Insights into the Interaction Mechanism Underlying the Adsorption and Retention of Heavy Metal Ions by Humic Acid

The mobility and distribution of heavy metal ions (HMs) in aquatic environments are significantly influenced by humic acid (HA), which is ubiquitous. A quantitative understanding of the interaction mechanism underlying the adsorption and retention of HMs by HA is of vital significance but remains elusive. Herein, the interaction mechanism between HA and different types of HMs (i.e., Cd(II), Pb(II), arsenate, and chromate) was quantitatively investigated at the nanoscale. Based on quartz crystal microbalance with dissipation tests, the adsorption capacities of Pb(II), Cd(II), As(V), and Cr(VI) ionic species on the HA surface were measured as ∼0.40, ∼0.25, ∼0.12, and ∼0.02 nmol cm-2, respectively. Atomic force microscopy force results showed that the presence of Pb(II)/Cd(II) cations suppressed the electrostatic double-layer repulsion during the approach of two HA surfaces and the adhesion energy during separation was considerably enhanced from ∼2.18 to ∼5.05/∼4.18 mJ m-2. Such strong adhesion stems from the synergistic metal-HA complexation and cation-π interaction, as evidenced by spectroscopic analysis and theoretical simulation. In contrast, As(V)/Cr(VI) oxo-anions could form only weak hydrogen bonds with HA, resulting in similar adhesion energies for HA-HA (∼2.18 mJ m-2) and HA-As(V)/Cr(VI)-HA systems (∼2.26/∼1.96 mJ m-2). This work provides nanoscale insights into quantitative HM-HA interactions, improving the understanding of HMs biogeochemical cycling.

Efficiency and mechanism of phosphate adsorption and desorption of a novel Mg-loaded biochar material

Phosphate removal is complicated by the need for resource recovery. Biochar shows promise for efficient phosphate adsorption, but it must be modified to enhance its adsorption capacity. In this work, magnesium (Mg)-loaded biochar was synthesized through a two-step dipping and calcination process, and the MgBC600 product was used to adsorb phosphate from simulated water and biogas slurry wastewater. The phosphate adsorption capacity of Mg-loaded biochar was 109.35 mg/g, which was 12 times higher than that of unmodified biochar. The R2 of the Langmuir and pseudo-second-order kinetic models were 0.988 and 0.990, respectively, which fitted the phosphate adsorption process of MgBC600. Phosphate adsorption by MgBC600 was a spontaneous and endothermic process. The adsorption mechanism study showed that phosphate adsorption was controlled by the formation and electrostatic attraction of MgHPO4. In addition, 98% of chemically adsorbed phosphate was released after regeneration. Using phosphate-adsorbed MgBC600 as a soil amendment, Arabidopsis thaliana was 1.47 times higher than that in the biochar-only group, demonstrating that this is a promising strategy for enhancing phosphate adsorption efficiency and adsorbent recycling.

Evaluation of a pH- and time-dependent model for the sorption of heavy metal cations by poultry litter-derived biochar

Common isotherm and kinetic models cannot describe the pH-dependent sorption of heavy metal cations by biochar. In this paper, we evaluated a pH-dependent, equilibrium/kinetic model for describing the sorption of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) by poultry litter-derived biochar (PLB). We performed sorption experiments across a range of solution pH, initial metal concentration, and reaction time. The sorption of all five metals increased with increasing pH. For Cd, Cu, and Pb, kinetics experiments demonstrated that sorption rates were greater at pH 6.5 than at pH 4.5. For each metal, all sorption data were described using single set of four adjustable parameters. Sorption edge and isotherm data were well described with R2 > 0.93 in all cases. Time-dependent sorption was well described (R2 ≥ 0.90) for all metals except Pb (R2 = 0.77). We then used the best-fit model parameters to calculate linear distribution coefficients (KD) and equilibration times as a function of pH and initial solution concentration. These calculations provide a more robust way of characterizing biochar affinity for metal cations than Freundlich distribution coefficients or Langmuir sorption capacity. Because this model can characterize metal cation sorption by biochar across a wider range of reaction conditions than traditional isotherm or kinetic models, it is better suited for estimating metal cation/biochar interactions in engineered or natural systems.

Enhanced removal performance of magnesium-modified biochar for cadmium in wastewaters: Role of active functional groups, processes, and mechanisms

In this study, a series of biochar products with different active functional groups were developed by one-pot coprecipitation method, including magnesium-modified biochar (MgBC) and functional group-grafted MgBC (Cys@MgBC, Try@MgBC, and Glu@MgBC), for effective adsorption of cadmium (Cd(II)) from wastewaters. These biochars exhibited excellent removal performance for Cd(II), particularly Cys@MgBC, whose maximum Cd(II) adsorption capacity reached 223.7 mg g-1. The highly active and weakly crystalline Mg could adsorb Cd(II) through precipitation and ion exchange, which was further promoted by the introduced functional groups through complexation and precipitation. After 120 d of natural process, the immobilization efficiency of Cd(II) by Cys@MgBC, Try@MgBC, and Glu@MgBC was still maintained at 98.7%, 95.2%, and 82.7% respectively. This study proposes and clarifies the complexation mechanism of functional group-grafted Mg-modified biochar for heavy metals, providing new insights into the practical application of these biochars.

Polyamidoamine Dendrimers Functionalized Water-Stable Metal-Organic Frameworks for Sensitive Fluorescent Detection of Heavy Metal Ions in Aqueous Solution

In this work, polyamidoamine (PAMAM)-functionalized water-stable Al-based metal-organic frameworks (MIL-53(Al)-NH2) were proposed with enhanced fluorescence intensity, and used for the sensitive detection of heavy metal ions in aqueous solution. The size and morphology of MIL-53(Al)-NH2 were effectively optimized by regulating the component of the reaction solvents. PAMAM dendrimers were subsequently grafted onto the surface with glutaraldehyde as a cross-linking agent. It was found that the size and morphology of MIL-53(Al)-NH2 have great influence on their fluorescence properties, and PAMAM grafting could distinctly further improve their fluorescence intensity. With higher fluorescence intensity, the PAMAM-grafted MIL-53(Al)-NH2 showed good linearity (R2 = 0.9925-0.9990) and satisfactory sensitivity (LOD = 1.1-8.6 μmol) in heavy metal ions determination. Fluorescence enhancement and heavy metal ions detection mechanisms were discussed following the experimental results. Furthermore, analogous water-stable Materials of Institute Lavoisier (MIL) metal-organic frameworks such as MIL-53(Fe)-NH2 were also proved to have similar fluorescence enhancement performance after PAMAM modification, which demonstrates the universality of the method and the great application prospects in the design of PAMAM-functionalized high-sensitivity fluorescence sensors.

Removal of Cd2+ from wastewater to form a three-dimensional fiber network using Si-Mg doped industrial lignin-based carbon materials

In this study, SiMg doped industrial lignin-based carbon materials (SLCs) were prepared by water bath silicification and MgCl₂ activation to remove Cd²⁺ from aqueous solutions. What's more, the doping of SiMg jointly promoted the excellent physicochemical properties of the material, e.g., high specific surface area, good pore volume, and numerous oxygen-containing groups. The Cd²⁺ batch adsorption experiments proved that SLCs have good Cd²⁺ removal capacity within pH 3-7, and the adsorption model demonstrated the adsorption process as a physicochemically complex process. The maximum adsorption of Cd²⁺ in the SLC was 665.35 mg/g, and the contributing factors to the removal of Cd²⁺ were as follows: ion exchange (59.36 %) > Cd²⁺ precipitation (24.93 %) > oxygen-containing functional group complexation (14.79 %) > Cd²⁺-π interactions (0.92 %). In addition, the complexation of SiO, MgO, and Cd precipitates allowed the formation of a three-dimensional fiber mesh structure. The application of SLCs has the potential to eliminate Cd²⁺ pollution in water bodies, and its preparation is simple and environmentally friendly. Finally, this study provides a theoretical basis for an in-depth understanding of the mechanism of heavy metal adsorption by inorganic nonmetals in combination with metal oxides.

Synthesis of Fe-THC MOFs and functionalizing MOFs by MXenes for the selective removal of lead(ii) ions from wastewater

The elimination of heavy metals, especially lead, from wastewater is vital for the environment and human health and using a proper adsorbent to achieve this goal is highly desirable. Initially, Fe-THC MOF was prepared using a simple method and functionalized using MXene for efficient, rapid, and selective elimination of lead. Different characterization tools demonstrated that Fe-THC MOF and its composite Fe-THC/MXene were successfully prepared. The adsorption outcomes showed that the maximum sorption capability was 674 mg g^-1 at 305 K and pH 4.5. The sorption kinetics obeys the pseudo-second-order kinetic model, and the sorption isotherms fit the Langmuir isotherm model. This finding suggests monolayer sorption on Fe-THC/MXene, and the rate-controlling step is chemisorption. Thermodynamic findings exhibit that sorption was a spontaneous and exothermic process. The sorption process can selectively adsorb Pb ions from aqueous media. After five adsorption-desorption tests, the adsorption efficiency of Fe-THC/MXene was still high. The sorption mechanism of lead on Fe-THC was mainly due to the interaction of lead ions with -F and -O ions and porosity of the Fe-THC/MXene composite. The -O and -F ions were derived from MXene, while the porosity was derived from the MOFs of composites. These findings confirmed that Fe-THC/MXene enables rapid, efficient, and selective elimination of lead from wastewater, which is of practical importance.

Modified biochar/humic substance/fertiliser compound soil conditioner for highly efficient improvement of soil fertility and heavy metals remediation in acidic soils

Fertile and uncontaminated soil with appropriate pH is crucial in terms of the agricultural sustainable development. Herein, a compound soil conditioner containing chitosan modified straw biochar (CBC), kitchen waste compost product-derived humic substance (HS), NPK compound fertiliser (NPK-CF) was prepared to simultaneously adjust acidic soil pH, improve fertility, and immobilize heavy metal. The results exhibited that the best Pb and NH₄⁺ adsorption performance was obtained in CBC with chitosan:biochar of 1:5. Then, the acid soil pH was improved from 5.03 to 6.66 in the presence of CBC/HS (5:5) with 3% addition weight (the mass ratio of conditioner to soil). Meanwhile, compared with the control, the contents of organic matter, available nitrogen, and available phosphorus significantly increased by 52.4%, 92.6%, and 136.3%, respectively. Moreover, Pb was highly efficient immobilised by CBC, and the concentration of Pb in the soil was decreased by 55.2%. The optimal growth trend of ryegrass was obtained in the presence of 3% addition weight (the mass ratio of conditioner to soil) CBC/HS (CBC:HS = 5:5) combined with 60% of the recommended NPK-CF application weight, which was mainly contributed by the improvement of the soil microbial abundance and community structure diversity. The addition of CBC/HS could effectively reduce the addition of NPK-CF and contribute to simultaneous controlling nitrogen loss, releasing phosphorus, immobilising Pb, adjusting pH, improving soil quality and controlling nonpoint pollution.

Solvent-Free Synthesis of Magnetic Sewage Sludge-Derived Biochar for Heavy Metal Removal from Wastewater

The commonly used two-step and one-pot synthesis methods for producing biochar require the use of iron salt solutions, resulting in the undesirable consequences of energy consumption for dewatering and potential pollution risks. To address this drawback, a magnetic sewage sludge-derived biochar (MSBC-2) was synthesized by a solvent-free method in this study. The pseudo-second-order kinetic model and Langmuir model provided the best fit to the experimental data, implying a monolayered chemisorption process of Pb2+, Cd2+and Cu2+ onto MSBC-2. As the reaction temperature increased from 25 °C to 45 °C, the maximum adsorption capacities increased from 113.64 mg·g−1 to 151.52 mg·g−1 for Pb2+, from 101.01 mg·g−1 to 109.89 mg·g−1 for Cd2+ and from 57.80 mg·g−1 to 74.07 mg·g−1 for Cu2+, respectively. Thermodynamic parameters (ΔG0 < 0, ΔS0 > 0, ΔH0 > 0) revealed that the adsorption processes of all three metals by MSBC-2 were favourable, spontaneous and endothermic. Surface complexation, cation-π interaction, ion exchange and electrostatic attraction mechanisms were involved in the adsorption of Pb2+, Cd2+ and Cu2+ onto MSBC-2. Overall, this study will provide a new perspective for the synthesis of magnetic biochar and MSBC-2 shows great potential as an adsorbent for heavy metal removal.

Nano Modifications of Biochar to Enhance Heavy Metal Adsorption from Wastewaters: A Review

Biochar (BC) is a carbon-rich material that can be obtained by thermal decomposition of agricultural solid waste under oxygen-limited conditions. It has received increasing attention as a cost-effective sorbent to treat metal-contaminated water due to attributes such as high porosity and the presence of various functional groups. The heavy metal (HM) sorption and removal capacity of BC can be enhanced by developing novel biochar nanohybrids (BNHs) that can be produced via surface modification of BC with nanomaterials. Loading of nanomaterials on the biochar surface can improve its physicochemical properties through alterations in the functional group profile, porosity, and availability of active sites on the BC surface which can enhance the HM adsorption ability. This manuscript provides information on preparation of nano-based biochar hybrids emanating from the type of modifying agent for the removal of different HM ions from wastewaters, and the underlying mechanisms have been discussed. Further, this compilation discusses published literature depicting the influence of different processes of preparation on the physicochemical properties and adsorption capacity of nanobiochar hybrids. The potential risks of BNHs have been reviewed to effectively avoid the possible harmful impacts on the environment, and future research directions have been proposed.

Adsorption Characteristics of Modified Bamboo Charcoal on Cu(II) and Cd(II) in Water

With the development of industry in recent years, heavy metal contamination in water and substrate, which may pose a serious threat to human health if left untreated, has attracted increasing attention. Biochar is commonly used as an adsorbent/immobilizer for heavy metals in water and substrates because of its wide range of raw materials, low production cost, and good adsorption performance. In this paper, we selected abundant Moso bamboo as the raw material to make biochar (bamboo charcoal), modified bamboo charcoal using different methods to find the modified product with the best adsorption effect, assessed the adsorption performance of modified bamboo charcoal on Cu(II) and Cd(II) in solution, and investigated the effects of the solution concentration, adsorption time, pH, and temperature on the adsorption effect of KAM500-400-3 on Cu(II) and Cd(II). The effect of the solution concentration, adsorption time, pH, and temperature on the adsorption effect of KAM500-400-3 on Cu(II) and Cd(II) was investigated, and the adsorption mechanism of KAM500-400-3 on heavy metals Cu(II) and Cd(II) was analyzed by fitting the adsorption kinetics, adsorption isotherms, and adsorption thermodynamics. The adsorption/fixation characteristics of modified bamboo charcoal on heavy metals Cu(II) and Cd(II) in water and substrate were investigated. This study aimed to identify an effective material for the treatment of heavy metals in water and substrates and provide a reference for their application in practical engineering.

Resource utilization of rice husk biomass: Preparation of MgO flake-modified biochar for simultaneous removal of heavy metals from aqueous solution and polluted soil

In general, the remediation performance of heavy metals can be further improved by metal-oxide modified biochar. This work used MgO-modified rice husk biochar (MgO-5%@RHB-450 and MgO-5%@RHB-600) with high surface activity for simultaneous remediation and removal of heavy metals in soil and wastewater. The adsorption of MgO-5%@RHB-450/MgO-5%@RHB-600 for Cd(II), Cu(II), Zn(II) and Cr(VI) followed the pseudo-second order, with the adsorption capacities reaching 91.13/104.68, 166.68/173.22, 80.12/104.38 and 38.88/47.02 mg g^-1, respectively. The addition of 1.0% MgO-5%@RHB-450 and MgO-5%@RHB-600 could effectively decrease the CaCl₂-extractable Cd concentration (CaCl₂-Cd) by 66.2% and 70.0%, respectively. Moreover, MgO-5%@RHB-450 and MgO-5%@RHB-600 facilitated the transformation of exchangeable fractions to carbonate-bound and residual fractions, and reduced the exchangeable fractions by 8.1% and 9.6%, respectively. The mechanisms for the removal of heavy metals from wastewater by MgO-5%@RHB-450 and MgO-5%@RHB-600 mainly included complexation, ion exchange and precipitation, and the immobilization mechanisms in soil may be precipitation, complexation and pore filling. In general, this study provides high-efficiency functional materials for the remediation of heavy metal pollution.

Biochar admixture cement mortar fines for adsorptive removal of heavy metals in single and multimetal solution: Insights into the sorption mechanisms and environmental significance

The combined action of biochar and C-S-H (calcium-silicate-hydrate) in the cement mortars as adsorbents was explored for treating heavy metals from water. The biochar admixture cement mortars were ground to fines for use as adsorbents with the rationale that combined action of Ca, Si, Al etc. based industrial waste with conventional adsorbent biochar could enhance the removal efficiency of contaminants and therefore the overarching aim was to study the removal capacity for three selected heavy metals (Pb^2+, Cu²⁺ and Zn²⁺) commonly found in the aqueous waste stream. Batch adsorption was carried out on single and multi-metal systems to determine the removal efficiency under varied conditions such as pH, dosage of adsorbent, the effect of contact time and the initial concentration of the adsorbate. For Pb(II), Cu (II) and Zn(II), pH 5 was optimized for single and multi-metal batch sorption studies. A dosage of 20 mg for single metal and 70 mg for multi-metal of an adsorbent dose was found to be sufficient to remove about 70-90% of the three heavy metals in 25 mL solution. Langmuir model best described the isotherm data with maximum adsorption capacities of 476, 81, 123 mg/g for Pb²⁺, Cu²⁺ and Zn²⁺ for BC-40 during single metal adsorption, which were quite comparable to other C-S-H and cement-based adsorbents. The metal hydroxides precipitation, the ion exchange between the Ca²⁺ and metal ions and metal complexation were explained as plausible mechanisms for the heavy metal removal.

Preparation, adsorption performance and mechanism of MgO-loaded biochar in wastewater treatment: A review

Biochar is a low cost, porous and solid material with an extremely high carbon content, various types of functional groups, a large specific surface area and many other desirable characteristics. Thus, it is often used as an adsorbent or a loading matrix. Nano-magnesium oxide is a crystalline material with small particles and strong ion exchangeability. However, due to the high surface chemical energy, it easily forms agglomerates of particles. Therefore, to combine the advantages of biochar and magnesium, metal magnesium nanoparticles can be loaded onto the surface of biochar with different modification techniques, resulting in biochars with low cost and high adsorption performance to be used as an adsorption matrix (collectively referred to as Mg@BC). This review presents the effects of different Mg@BC preparation methods and synthesis conditions and summarizes the removal capabilities and adsorption mechanisms of Mg@BC for different types of pollutants in water. In addition, the review proposes the prospects for the development of Mg@BC to solve various problems in the future.

Ion exchange to immobilize Cd(II) at neutral pH into silicate matrix prepared by co-grinding kaolinite with calcium compounds

A novel silicate-based composite material was simply prepared by co-milling kaolinite and calcium compounds to endow the well studied clay minerals with active calcium for efficient removal of heavy metals. Batch experiments were carried out to investigate the main affecting factors such as raw material ratio, ball milling time, contact time, etc.. Even at a neutral solution pH, the silicate adsorbent exhibited excellent performance for the adsorption of Cd(II), reaching equilibrium in 30 min with a removal efficiency over 95%, and allowed a direct discharge of the treated solution without the need of acidic neutralization as usually used in the alkaline precipitation. A set of analytical methods including SEM/EDS and ²⁹Si MAS NMR etc. were used to analyze the adsorption mechanism of Cd(II), revealing that the adsorption process was mainly dominated by ion exchange to accommodate Cd ions inside silicate matrix, accompanied with partial hydroxide precipitation, rather than normally reported surface adsorption on pristine minerals. Furthermore, the as-prepared adsorption material exhibited similar excellent immobilization capacity for multiple heavy metals including Cu(II), Zn(II), Ni(II), Cd(II) and Mn(II). These findings provide a novel concept for the activation of the widely available cheap silicate minerals by the same widely available cheap calcium compounds and high contribution may be expected on its potentials to the environmental purification of heavy metal pollution in water and soil.

Magnesium ferrite-nitrogen-doped graphene oxide nanocomposite: effective adsorptive removal of lead(II) and arsenic(III)

Magnetic nanocomposites have received immense interest as adsorbents for water decontamination. This paper presents adsorptive properties of nitrogen-doped graphene oxide (N-GO) with magnesium ferrite (MgFe₂O₄) magnetic nanocomposite for removing lead(II) (Pb(II)and arsenite As(III) ions. Transmission electron microscope (TEM) image of synthesized nanocomposite revealed the wrinkled sheets of N-GO containing MgFe₂O₄ nanoparticles (NPs) with particle size of 5-15 nm distributed over its surface. This nanocomposite displayed higher BET surface area (72.2 m²g^-1) than that of pristine MgFe₂O₄ NPs (38.4 m²g^-1). Adsorption on the nanocomposite could be described by the Langmuir isotherm with the maximum adsorption capacities were 930 mg/g, and 64.1 mg/g for Pb(II) and As(III), respectively. Whereas, maximum removal efficiencies were observed to be 99.7 [Formula: see text] 0.2% and 93.5 [Formula: see text] 0.1% for Pb(II) and As(III), respectively. The study on the effect of coexisting anions on the adsorption of metal ions showed that the phosphate ions were potential competitors of Pb(II) and As(III) ions to adsorb on the nanocomposite. Significantly, the investigation on adsorption of metal ion in the presence of coexisting heavy metal ions indicated the preferential adsorption of Pb(II) ions as compared to Cd(II), Zn(II) and Ni(II) ions. The effectiveness of the nanocomposite to remove the metal ions in electroplating wastewater was demonstrated.

Highly efficient metal-organic frameworks adsorbent for Pd(II) and Au(III) recovery from solutions: Experiment and mechanism

With the boom of modern industry, the demand for precious metals palladium (Pd) and gold (Au) is increasing. However, the discharge of Pd(II) and Au(III) wastewater has caused environmental pollution and shortage of resources. Here, a new metal-organic frameworks adsorbent (MOF-AFH) was synthesized to efficiently separate Pd(II) and Au(III) from the water. The adsorption behavior of Pd(II) and Au(III) was explored at the same time. When gold and palladium are adsorbed separately, the adsorption capacity of gold and palladium is 389.02 mg/g and 191.27 mg/g, respectively. The equilibration time is 3 h. When gold and palladium coexist, the adsorption capacities of Au(III) and Pd(II) are 238.71 and 115.02 mg/g, respectively. The experimental results show that the adsorption of Pd(II) and Au(III) on MOF-AFH is a single-layer chemical adsorption, which is an endothermic process. MOF-AFH has excellent selectivity and after MOF-AFH is repeatedly used 4 times, the removal effect can still reach more than 90%. The adsorption mechanisms include reduction reaction and chelation with N and O-containing functional groups on the adsorbent. There is also electrostatic interaction for Au(III) adsorption. The adsorbent can be used to efficiently recover gold and palladium from wastewater.

Hydrogen peroxide contributes to cadmium binding on root cell wall pectin of cadmium-safe rice line (Oryza sativa L.)

Cell wall pectin is essential for cadmium (Cd) accumulation in rice roots and hydrogen peroxide (H₂O₂) plays an important role as a signaling molecule in cell wall modification. The role of H₂O₂ in Cd binding in cell wall pectin is unclear. D62B, a Cd-safe rice line, was found to show a greater Cd binding capacity in the root cell wall than a high Cd-accumulating rice line of Wujin4B. In this study, we further investigated the mechanism of the role of H₂O₂ in Cd binding in root cell wall pectin of D62B compared with Wujin4B. Cd treatment significantly increased the H₂O₂ concentration and pectin methyl esterase (PME) activity in the roots of D62B and Wujin4B by 22.45-42.44% and 12.15-15.07%, respectively. The H₂O₂ concentration and PME activity significantly decreased in the roots of both rice lines when H₂O₂ was scavenged by 4-hydroxy-Tempo. The PME activity of D62B was higher than that of Wujin4B. The concentrations of high and low methyl-esterified pectin in the roots of D62B significantly increased when exposed to Cd alone but significantly decreased when exposed to Cd and exogenous 4-hydroxy-Tempo. No significant difference was detected in Wujin4B. Exogenous 4-hydroxy-Tempo significantly decreased the Cd concentration in the cell wall pectin in both rice lines. The modification of H₂O₂ in Cd binding was further explored by adding H₂O₂. The maximum Cd adsorption amounts on the root cell walls of both rice lines were improved by exogenous H₂O₂·H₂O₂ treatment significantly influenced the relative peak area of the main functional groups (hydroxyl, carboxyl), and the groups intensely shifted after Cd adsorption in the root cell wall of D62B, while there was no significant difference in Wujin4B. In conclusion, Cd stress stimulated the production of H₂O₂, thus promoting pectin biosynthesis and demethylation and releasing relative functional groups involved in Cd binding on cell wall pectin, which is beneficial for Cd retention in the roots of Cd-safe rice line.

Enhancing Cd(II) adsorption on rice straw biochar by modification of iron and manganese oxides

Metal oxide-modified biochar showed excellent adsorption performance in wastewater treatment. Iron nitrate and potassium permanganate were oxidative modifiers through which oxygen-containing groups and iron-manganese oxides could be introduced into biochar. In this study, iron-manganese (Fe-Mn) oxide-modified biochar (BC-FM) was synthesized using rice straw biochar, and the adsorption process, removal effect, and the mechanism of cadmium (Cd) adsorption on BC-FM in wastewater treatment were explored through batch adsorption experiments and characterization (SEM, BET, FTIR, XRD, and XPS). Adsorption kinetics showed that the maximum adsorption capacity of BC-FM for Cd(II) was 120.77 mg/g at 298 K, which was approximately 1.5-10 times the amount of adsorption capacity for Cd(II) by potassium-modified or manganese-modified biochar as mentioned in the literature. The Cd(II) adsorption of BC-FM was well fit by the pseudo-second-order adsorption and Langmuir models, and it was a spontaneous and endothermic process. Adsorption was mainly controlled via a chemical adsorption mechanism. Moreover, BC-FM could maintain a Cd removal rate of approximately 50% even when reused three times. Cd(II) capture by BC-FM was facilitated by coprecipitation, surface complexation, electrostatic attraction, and cation-π interaction. Additionally, the loaded Fe-Mn oxides also played an important role in the removal of Cd(II) by redox reaction and ion exchange in BC-FM. The results suggested that BC-FM could be used as an efficient adsorbent for treating Cd-contaminated wastewater.

Detection and Prediction of HMS from Drinking Water by Analysing the Adsorbents from Residuals Using Deep Learning

Contamination HM is an important issue associated with the environment, and it requires suitable steps for the reduction of HMs in water at an acceptable ratio. With modern technologies, this could be possible by enabling the carbon adsorbents to adsorb the pollutions via deep learning strategies. In this paper, we develop a model on detection and prediction of presence of HMs from drinking water by analysing the adsorbents from residuals using deep learning. The study uses dense neural networks or DenseNets to analyse the microscopic images of the residual adsorbents. The study initially preprocesses and extracts features using standardised procedure. The DenseNets are used finally for detection purpose, and it is trained and tested with standard set of microscopic images. The experimental results are conducted to test the efficacy of the deep learning model on detecting the HM composition. The results of simulation show that the proposed deep learning model achieves 95% higher rate of detecting the HM composition from the adsorption residuals than other methods.

Removal of heavy metals from wastewaters with biochar pyrolyzed from MgAl-layered double hydroxide-coated rice husk: Mechanism and application

This study reports a MgAl-LDH rice husk biochar composite (MgAl-LDH@RHB) with a regular hydrotalcite structure synthesized by a simple hydrothermal method, which was then used to remove Cd(II) and Cu(II) from water. The influencing factors on the adsorption performance were determined through batch adsorption experiments, and the adsorption characteristics and cycling capacity were evaluated with eight models and adsorption-desorption experiments. The results showed that the adsorption of Cd(II) and Cu(II) by MgAl-LDH@RHB conformed to the Langmuir-Freundlich model and PSO kinetics model, indicating single-layer chemical adsorption. In addition, the experimental maximum adsorption capacities for Cd(II) and Cu(II) were 125.34 and 104.34 mg g^-1, respectively. The adsorption of Cd(II) and Cu(II) by MgAl-LDH@RHB was dominated by surface precipitation and ion exchange. The findings reveal the mechanism for the heavy metal removal by MgAl-LDH@RHB and provide a theoretical reference for agricultural waste disposal and water pollution control.

Unraveling the molecular mechanisms of Cd sorption onto MnOx-loaded biochar produced from the Mn-hyperaccumulator Phytolacca americana

Engineered biochar represents a promising material for green remediation practices. In this paper, we present an innovative approach to produce MnO_x-loaded biochars by pyrolyzing the biomass of a Mn-hyperaccumulator species (Phytolacca americana). Batch sorption and stirred-flow kinetic experiments were combined with spectroscopic techniques to elucidate the mechanisms behind the Cd sorption onto those biochars, named here as PABCs. The incorporation of MnO_x into the PABCs increased their surface densities of oxygen-containing functional groups. The average Mn leaching (< 9%) from PABCs was lower than that measured for the non-pyrolyzed biomass of P. americana (30-43%). PABCs pyrolyzed at 500 °C had Cd sorption capacities as high as 212-337 mg/g, which achieved by far the best performance reported for biochar materials. The stirred-flow experiments showed that MnO_x loading was instrumental in increasing both the Cd sorption onto PABCs as well as its irreversibility. Extended X-ray absorption fine structure spectroscopy revealed that the Cd immobilization occurred mainly through its association with organic matter (Cd-OM) and, to a lesser extent, with carbonate (CdCO₃) and MnO_x (Cd-MnO_x). In short, MnO_x-loaded biochar prepared from the biomass of a Mn-hyperaccumulator species proved to be an effective, sustainable, and eco-friendly material for remediating Cd-contaminated waters.

Enhanced adsorption of metal ions onto Vetiveria zizanioides biochar via batch and fixed bed studies

The study highlights the potential of Vetiveria Zizanioides derived biochar for heavy metal removal in multicomponent systems. Biochar efficiency varies with pH, metal ion concentration and residence time. Maximum removal efficiency was found to be 66.34, 67.23, 46.54, 69.92, 68.23 and 63.34% for Arsenic, Copper, Nickel, Cadmium, Lead and Chromium at 90 min respectively. Ternary system revealed that Copper ions have inhibitory effect on Lead ions and have lower adsorption capacity than binary system. Multicomponent isotherm model was used to analyse simultaneous adsorption of metal ions and shows a good fit with modified Langmuir model for binary and ternary systems. Fixed-bed column was tested for scale-up feasibility and maximum adsorption capacity of 139, 130, and 123 mg/g for Lead, Copper, and Nickel ions were obtained at 1.5 L/h and a bed height of 12 cm. In fixed bed column, multicomponent sequence provides more protection against premature exhaustion of biochar.

Efficient and selective removal of Pb(ii) from aqueous solution by a thioether-functionalized lignin-based magnetic adsorbent

The effective and selective removal of heavy metal ions from sewage is a major challenge and is of great significance to the treatment and recovery of metal waste. Herein, a novel magnetic lignin-based adsorbent L@MNP was synthesized by a thiol-ene click reaction under ultraviolet (UV) light irradiation. Multiple characterization techniques, including Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), elemental analysis, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed the formed nano-morphology and structure of L@MNP. The effects of pH, contact time, initial metal concentration and temperature on the batch adsorption of Pb(ii) by L@MNP were investigated. Due to the existence of sulfur and oxygen-containing sites, the maximum adsorption capacity of L@MNP for Pb(ii) could reach 97.38 mg g^-1, while the adsorption equilibrium was achieved within 30 min. The adsorption kinetics and isotherms were well described by the pseudo-second-order model and Langmuir model, respectively, suggesting a chemical and monolayer adsorption process. In addition, L@MNP showed a high adsorption selectivity (k _Pb = 0.903) toward Pb(ii) in the presence of other co-existing metal ions. The experimental results also revealed that L@MNP displayed structural stability, ease of recovery under an external magnetic field, and acceptable recyclability after the fifth cycle. Considering its facile preparation, low cost and high adsorption efficiency, the developed L@MNP adsorbent demonstrated great potential in removing heavy metal ions from wastewater.

Quantitative analysis on the mechanism of Cd2+ removal by MgCl2-modified biochar in aqueous solutions

In this study, a pristine biochar (BC) and MgCl₂-modified biochar (MBC) were prepared using Pennisetum sp. straw for removing Cd²⁺ from aqueous solutions. Scanning electron microscope (SEM) imaging combined with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), as well as the surface area and porosity analyses were used to reveal the physico-chemical characteristics of the pristine and modified adsorbents. Results suggested that MgCl₂ impregnation during the synthesis had enhanced the specific surface area and pore volume of the biochar. Batch adsorption experiments indicated that the Cd²⁺ adsorption data of MBC fitted the Langmuir isothermal and pseudo-second order kinetic models, indicating a chemical adsorption was undergoing in the system. The maximum adsorption capacity of Cd²⁺ on MBC was 763.12 mg/g, which was 11.15 times higher than that of the pristine BC. The Cd²⁺ removal by MBC was mainly attributed to the mechanisms in an order: Cd(OH)₂ precipitation (73.43%) > ion exchange (22.67%) > Cd²⁺-π interaction (3.88%), with negligible contributions from functional group complexation, electrostatic attraction and physical adsorption. The MBC could thus be used as a promising adsorbent for Cd²⁺ removal from aqueous solutions.

Calcium-Modified Fe3O4 Nanoparticles Encapsulated in Humic Acid for the Efficient Removal of Heavy Metals from Wastewater

Ca-modified Fe₃O₄ nanoparticles encapsulated in humic acid (HA-Ca/Fe₃O₄) were produced using a co-precipitation method. Furthermore, the adsorption performance of HA-Ca/Fe₃O₄ as well as the effect of coexisting ions and mechanisms were evaluated. A good description of the adsorption process was given using pseudo-second-order kinetic and Langmuir models. The adsorption capacities of HA-Ca/Fe₃O₄ for Pb²⁺, Cu²⁺, and Cd²⁺ were 208.33, 98.33, and 99.01 mg g^-1, respectively. The 0.02-0.1 times concentrations in alkali and alkaline-earth metals promoted Pb²⁺ and Cd²⁺ adsorption; however, any concentration of alkali and alkaline-earth metals inhibited Cu²⁺-ion adsorption, probably owing to the differences in ionic radii between the interfering and heavy-metal ions. Pb²⁺, Cu²⁺, and Cd²⁺ removal using HA-Ca/Fe₃O₄ occurred via ion exchange, complexation of O-containing functional groups, mineral precipitation, and π-electron coordination. A method was proposed to calculate the contribution of these mechanisms to the adsorption process. In practice, HA-Ca/Fe₃O₄ can remove 99% Pb²⁺ and 91% Cu²⁺ and Cd²⁺ from real wastewater samples. Following five adsorption-desorption cycles, HA-Ca/Fe₃O₄ adsorption capacity did not change significantly. The aforementioned results indicated that HA-Ca/Fe₃O₄ presented a good potential in removing heavy metals in wastewater.

Preparation and Characterization of Phosphoric Acid-Modified Biochar Nanomaterials with Highly Efficient Adsorption and Photodegradation Ability

Phosphoric acid-modified biochar (PMBC) was prepared using biochar (BC) as the carbon source and phosphoric acid as the activating agent. The PMBC exhibited an ordered vessel structure after deashing treatment, but the sidewalls became much rougher, the polarity (O/C atomic ratio of BC = 0.2320 and O/C atomic ratio of PMBC = 0.1604) decreased, and the isoelectric points (PI of BC = 5.22 and PI of PMBC = 5.51) and specific surface area (SSA of BC = 55.322 m²/g and SSA of PMBC = 62.285 m²/g) increased. The adsorption characterization of the removal of sulfadiazine (SDZ) from PMBC was studied. The adsorption of SDZ by PMBC was in accordance with the Langmuir isotherm model and the pseudo-second-order kinetics model, and the adsorption thermodynamics were shown as Gibbs free energy < 0, an enthalpy change of 19.157 kJ/mol, and an entropy change of 0.0718 kJ/(K·mol). The adsorption of SDZ by PMBC was a complicated monolayer adsorption that was spontaneous, irreversible, and endothermic, and physical adsorption and chemical adsorption occurred simultaneously. The adsorption process was controlled by microporous capture, electrostatic interactions, hydrogen-bond interactions, and π-π interactions. PMBC@TiO₂ photocatalysts with different mass ratios between TiO₂ and PMBC were prepared via the in situ sol-gel method. PMBC@TiO₂ exhibited both an ordered vessel structure (PMBC) and irregular particles (TiO₂), and it was linked via Ti-O-C bonds. The optimal mass ratio between TiO₂ and PMBC was 3:1. The removal of SDZ via PMBC@TiO₂ was dependent on the coupling of adsorption and photocatalysis. The PMBC-enhanced photocatalytic performance of PMBC@TiO₂ resulted in a higher absorption of UV and visible light, greater generation of reactive oxygen species, high levels of adsorption of SDZ on PMBC, and the conjugated structure and oxygen-containing functional groups that promoted the separation efficiency of the hole-electron pairs.

Phenylthiosemicarbazide-functionalized UiO-66-NH2 as highly efficient adsorbent for the selective removal of lead from aqueous solutions

A novel metal-organic framework (UiO-66-PTC) for efficient removal of Pb²⁺ ions from wastewater has been prepared by using 4-phenyl-3-thiosemicarbazide as the modifier. Various characterizations showed that UiO-66-PTC was successfully synthesized. The absorption results showed that the maximum adsorption capacity of Pb(II) is 200.17 mg/g at 303 K and optimal pH 5. The adsorption kinetic follows the pseudo-second-order model and the adsorption isotherms fit the Langmuir model. This shows that Pb(II) is a single-layer adsorption on the surface of the adsorbent and the rate-controlling step is chemical adsorption. The thermodynamic results show that the adsorption process can proceed spontaneously, belong to the exothermic reaction. The adsorbent can selectively uptake lead ions from wastewater containing multiple interfering ions. After four adsorption and desorption cycles, the adsorption efficiency is still high. The adsorption mechanism of Pb(II) on the adsorbent is mainly through the chelation of Pb(II) with N and S atoms. These results indicate that UiO-66-PTC is an effective material for efficiently and selectivity removal of Pb(II) from solution, which is of practical significance.

Potassium phosphate/magnesium oxide modified biochars: Interfacial chemical behaviours and Pb binding performance

Removal of lead (Pb) from aqueous solutions by biochar is a promising method. In this study, wheat straw biochar (WBC) was modified by phosphate/magnesium via pre-treatment of biomass and post-treatment of biochar, noting as WBC_PMA and WBC_PMB, respectively. Based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, phosphate/magnesium chemically bound to the structures of biochar surface, increasing the contents of polar groups (i.e., -COOH and -OH) and phosphorus-containing compounds, mainly Mg₃(PO₄)₂ and Mg₂P₂O₇. Owing to pyrolysis process enhancing loading ability of phosphate/magnesium, WBC_PMA possessed more active functional groups than WBC_PMB. Results showed that maximum sorption capacity of Pb was improved by modifications, following the sequence of WBC_PMA (470.09 mg/g) > WBC_PMB (308.39 mg/g) > WBC (59.93 mg/g). Pseudo-second-order kinetics and thermodynamics study indicated that chemisorption was involved in sorption process. Precipitation, complexation and cation exchange dominated Pb sorption and the corresponding contributions accounted for 17.89-32.73%, 28.84-46.22%, and 21.05-53.27%, respectively. Additionally, desorption characteristics of Pb illustrated that WBC_PMA owned more prominent stabilization ability than that of WBC and WBC_PMB. The findings of this study suggested that pre-modification method increased the contents of active groups in biochar and strengthened the removal efficiency of Pb ultimately. Due to the complexity of the actual Pb-containing wastewater environment, it was necessary to evaluate the effects of various factors on the stabilization performance of the pre-modified biochar in further.