Adsorption of Cu(II) and Cd(II) from aqueous solutions by ferromanganese binary oxide-biochar composites

The study on adsorption behavior of 2,4-DCP in solution by biomass carbon modified with CTAB-KOH

In this study, rice straw was used to prepare biomass carbon, which was modified with KOH and cetyltrimethylammonium bromide (CTAB) to obtain modified biomass carbon (MBC). The biomass carbon (BC) before and after modification was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR), and the surface morphology, crystal structure and surface group characteristic BC were explored. The specific surface area and micropores of the modified biomass carbon increased significantly, the crystallinity was higher, and the pore structure was more clearly found. The adsorption performance of MBC for 2,4-dichlorophenol (2,4-DCP) was investigated. The results showed that under the best adsorption conditions ((2,4-DCP concentration (200 mg/L), MBC dosage (50 mg), pH (5.5), and loading time (60 min), temperature (room temperature)), the removal rate of 2,4-DCP was up to 42.5%, and adsorption capacity was 85.13 mg/g. The adsorption of 2,4-DCP on MBC materials was better explained by the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model. It was believed that the adsorption of 2,4-DCP by MBC was the monolayer adsorption process on the uniform surface of MBC at high concentration, and there was no interaction between the 2,4-DCP and MBC adsorbate during this process.

Adsorption of As(V) by the Novel and Efficient Adsorbent Cerium-Manganese Modified Biochar

Arsenic has become a global concern in water environment, and it is essential to develop efficient remediation methods. In this study, a novel adsorbent by loading cerium and manganese oxide onto wheat straw-modified biochar (MBC) was manufactured successfully aiming to remove arsenic from polluted water. Through scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), and other techniques, it was found the loading of cerium and manganese oxide on MBC played a significant role in As(V) adsorption. The results of the batch test showed that the adsorption of MBC followed the pseudo-second order kinetics and Langmuir equation. The adsorption capacity of MBC was 108.88 mg As(V)/g at pH = 5.0 (C0 = 100 mg/L, dosage = 0.5 g/L, T = 298 K) with considerable improvement compared to the original biochar. Moreover, MBC exhibited excellent performance over a wide pH range (2.0~11.0). Thermodynamics of the sorption reaction showed that the entropy (ΔS), changes of enthalpy (ΔH) and Gibbs free energy (ΔG), respectively, were 85.88 J/(moL·K), 22.54 kJ/mol and −1.33 to −5.20 kJ/mol at T = 278~323 K. During the adsorption, the formation of multiple complexes under the influence of its abundant surface M-OH (M represents the Ce/Mn) groups involving multiple mechanisms that included electrostatic interaction forces, surface adsorption, redox reaction, and surface complexation. This study indicated that MBC is a promising adsorbent to remove As(V) from polluted water and has great potential in remediating of arsenic contaminated environment.

Properties and adsorption mechanism of magnetic biochar modified with molybdenum disulfide for cadmium in aqueous solution

In this paper, we present the preparation of MoS₂-modified magnetic biochar (MoS₂@MBC) as a novel adsorbent by a simple hydrothermal method. MoS₂@MBC contains abundant S-containing functional groups that facilitate efficient Cd(II) removal from aqueous systems. We employed various characterization techniques to explore the morphology, surface area, and chemical composition of MoS₂@MBC; these included Brunauer-Emmett-Teller analysis scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction,. The results indicated the successful decoration of the surface of MoS₂@MBC with iron and MoS₂, and a higher surface area of MoS₂@MBC than that of unmodified biochar. Moreover, adsorption properties including thermodynamics and kinetics were investigated along with the effects of pH, humic acid, and ionic strength on the Cd(II) adsorption onto MoS₂@MBC. The O-, C-, S-, and Fe-containing functional groups on the surface of MoS₂@MBC led to an electrostatic attraction of Cd(II) and strong Cd-S complexation. The Langmuir and pseudo second-order models fitted best for the batch adsorption experiments results. The adsorption capacity of MoS₂@MBC (139 mg g^-1 on the basis of the Langmuir model) was 7.81 times higher than that of pristine biochar. The adsorption process was found to be pH-dependent. The experimental results indicated that MoS₂@MBC is an effective adsorbent for removing Cd(II) from water solutions. Further, the adsorption process involved the complexation of Cd(II) with oxygen-based functional groups, ion exchange, electrostatic attraction, Cd(II)-π interactions, metal-sulfur complexation, and inner-surface complexation. This work provides new insights into the Cd(II) ions removal from water via adsorption. It also demonstrates that MoS₂@MBC is an efficient and economic adsorbent to treat Cd(II)-contaminated water.

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

Six types of biochar (BSB, CSB, FSB, CFSB, MSB, and TSB) were prepared from different raw materials by loading magnesium ions (Mg²⁺) via an impregnation process. The adsorption kinetics and thermodynamics of heavy metals at high concentrations were analyzed. The adsorption mechanisms were investigated by zeta potential, scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic absorption spectroscopy analyses. The adsorption of heavy metals by BSB, CSB, FSB, CFSB, MSB, and TSB conformed to the Langmuir model and PS-order. The maximum theoretical saturation adsorption capacities for Cd(II), Cu(II), and Pb(II) were 333.33, 238.10, 75.19, 96.15, 66.23, and 185.19 mg·g^-1; 370.37, 294.12, 111.11, 169.49, 84.75, and 217.39 mg·g^-1; and 302.58, 200.00, 61.73, 90.91, 54.47, and 166.67 mg·g^-1, respectively. According to the analysis of the contribution of adsorption, the adsorption process was mainly controlled by cation-π interactions, ion exchange, mineral precipitation, and functional group interactions. Biochars contain ash, functional groups and load a large number of Mg²⁺, which can form complexes with metal ions and perform strong ion exchange; therefore, mineral precipitation and cation exchange played dominant roles in the adsorption process. The prepared Mg-loaded biochars presented in this research showed excellent adsorption properties for heavy metals and have great potential for practical application; in particular, BSB had the strongest adsorption capacity for the three heavy metal ions.

Facile Synthesis of Cauliflower Leaves Biochar at Low Temperature in the Air Atmosphere for Cu(II) and Pb(II) Removal from Water

In this study, a facile and low-cost method for biochar (CLB) preparation from vegetable waste (cauliflower leaves) was developed at a low temperature (120 °C) in the air atmosphere. The prepared mechanism, adsorption mechanism, and performance of CLB for Cu(II) and Pb(II) sorption were investigated using Scanning electron microscopy- energy dispersive X-ray spectroscopy(SEM-EDS), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), and a series of sorption experiments. Then the CLB was subjected to single and double element sorption studies to examine the effect of pH value on the Cu(II)/Pb(II) sorption capacities and then competitive sorption priority. There are both more hydroxyl (–OH) and carboxyl (–COOH) functional groups on the surface of CLB compared to those from control (without H₃PO₄ impregnation), resulting in more ion exchanges and complexation reaction for CLB with Cu(II) and Pb(II). Besides, the phosphorus-containing groups (e.g., P = OOH, P = O.), which newly formed with H₃PO₄ impregnation, could also enhance sorption, especially for Pb(II), this way leaded to its adsorption and precipitation as Pb₅(PO₄)₃OH crystals. The performance of maximum adsorption capacities of CLB toward Cu(II) and Pb(II) were 81.43 and 224.60 mg/g, respectively. This sorption was slightly pH-dependent, except that the sorption capacity improved significantly as the pH value of the solution increased from 2 to 4. Competitive sorption experiment confirmed that Pb(II) had a higher sorption priority than Cu(II).

Microwave-assisted preparation of manganese dioxide modified activated carbon for adsorption of lead ions

In this study, manganese dioxide was evenly distributed on the surface of activated carbon (AC), and the porous structure of AC and the surface functional groups of manganese dioxide were used to adsorb the heavy metal ion Pb(II). The advantages of microwave heating are fast heating and high selectivity. The mole ratio control of the AC and MnO₂ in 1:0.1, microwave heating to 800 °C, heat preservation for 30 min. The maximum adsorption capacity of the MnO₂-AC prepared by this method on Pb(II) can reach 664 mg/L at pH = 6. It can be observed by scanning electron microscope (SEM) that manganese dioxide particles are dispersed evenly on the surface and pore diameter of AC, and there is almost no agglomeration. The specific surface area was 752.8 m²/g, and the micropore area was 483.9 m²/g. The adsorption mechanism was explored through adsorption isotherm, adsorption kinetics, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). It is speculated that the adsorption mechanism includes electrostatic interaction and specific adsorption, indicating that lead ions enter into the void of manganese dioxide and form spherical complexes. The results showed that the adsorption behavior of Pb(II) by MnO₂-AC was consistent with the Langmuir adsorption model, the quasi-second-order kinetic model, and the particle internal diffusion model.

Struvite-supported biochar composite effectively lowers Cu bio-availability and the abundance of antibiotic-resistance genes in soil

The accumulation of heavy metals and the accelerated dissemination of antibiotic-resistance genes (ARGs) in soil receiving long-term manure application are causing worldwide concern. In this study, struvite-supported biochar composite (MAP/BC) obtained by N and P recovery from pig slurry with Mg(OH)₂-modified biochar (Mg(OH)₂/BC) was used as a novel amendment for the remediation of Cu- and ARG-contaminated agricultural soil. The effects of MAP/BC on Cu immobilization, ARG distribution, and the bacterial community in the soil were investigated simultaneously. The results showed that the mechanisms involved in the immobilization of Cu by MAP/BC included the formation of copper-phosphate precipitation and a surface complex. With a 10% MAP/BC modification, the acid-soluble Cu content in soil decreased by 0.47-fold at day 56 while the residual Cu content increased 1.41-fold. Meanwhile, the abundances of most of the target ARGs (tetX, tetT, tetW, tetG, ermB, sulI, sulII, and intlI) were reduced by 11.35-99.95%, and the abundance of total ARGs was reduced by 30.69%. The redundancy analysis indicated that the bio-available Cu content played a crucial role in the variations of both ARGs and bacterial communities. The network analysis further suggested that potential hosts of soil ARGs were mainly Firmicutes and Actinobacteria. The above results suggested that the application of MAP/BC can mitigate Cu and ARG pollution in manured soil.

Comparison of adsorption properties for cadmium removal from aqueous solution by Enteromorpha prolifera biochar modified with different chemical reagents

Using biochar to remove heavy metals from water is environmentally beneficial. In this study, three kinds of chemical reagents, including ZnCl₂, H₃PO₄ and KMnO₄, were introduced to modify the biochar derived from Enteromorpha prolifera. The performance of these modified biochar in removing Cadmium ions (Cd(II)) from water was investigated. The physicochemical properties of activated biochars were characterized by N₂-sorption, thermal gravity and differential thermal gravity (TG/DTG), scanning electron microscopy (SEM), elemental analysis and Fourier transform infrared spectroscopy (FTIR). The results showed that the removal rate of Cd(II) from water by EP biochar modified with H₃PO₄ was significantly increased, and the maximum adsorption capacity of Cd(II) reached to 423 mg/g for PBC. Moreover, the adsorption of Cd(II) from water by phosphoric acid modified biochar was very fast, and the saturation adsorption of Cd(II) was reached within 1 h. Compared with pseudo first-order model, pseudo secondary-order model was much more suitable for analyzing the adsorption kinetics data of Cd(II) onto KBC or ZBC. The adsorption of Cd(II) onto PBC was analyzed by the intra-particle diffusion kinetic model, where the value of R² was high as 0.98. The Langmuir model was fit for phosphoric acid modified biochar.

Effect of temperature and duration of pyrolysis on spent tea leaves biochar: physiochemical properties and Cd(II) adsorption capacity

We analyzed the effects of pyrolysis temperature and duration on the physiochemical properties and Cd(II) adsorption capacity of spent tea leaves (STL) biochar. The STL biochar was produced by pyrolysis at 300, 400, 500 and 600 °C for 1 and 2 h. The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S_BET), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios. Furthermore, the surface porosity of STL biochar increased, the density of oxygen-containing functional groups decreased, and the formation of aromatic structures was enhanced at higher pyrolysis temperatures. The adsorption of Cd(II) onto STL biochar fitted with the pseudo-second-order kinetics and Langmuir isotherms model. The STL biochar produced at 600 °C for 2 h showed the maximum Cd(II) adsorption capacity of 97.415 mg/g. In addition, Cd(II) adsorption was mainly physical and occurred in monolayers. Thus, STL biochar is a suitable low-cost adsorbent for wastewater treatment.

The characteristics of oestrone mobility in water and soil by the addition of Ca-biochar and Fe-Mn-biochar derived from Litchi chinensis Sonn

In this study, the effect of biochar (BC) derived from Litchi chinensis Sonn. and its modification, including Ca-biochar (Ca-BC) and Fe-Mn-biochar (Fe-Mn-BC), on the transportation of oestrone (E1) in water and soil was investigated. Fe-Mn-BC showed better adsorption ability than other types of biochar (BC, Ca-BC) under different conditions (humic acid, pH, ionic strength) in an aqueous environment. The maximum mass of sorbent at 298 K increased from 1.12 mg g^-1 (BC) to 4.18 mg g^-1 (Fe-Mn-BC). Humic acid had a greater impact on aqueous E1 adsorption on these biochars than did the pH and ionic strength. Fe-Mn-BC as a soil amendment had a great control of E1 transport in soil, and no leachate of E1 was observed in the column experiment. E1 mobility showed strong retardation in amended soil with Ca-BC (R_f = 11.2) compared with raw soil (R_f = 7.1). These results suggested that Fe-Mn-BC was more effective in controlling E1 transportation, and Fe-Mn-BC could be used as an alternative and inexpensive adsorbent to reduce E1 contaminants from water and soil.

Mechanisms for cadmium adsorption by magnetic biochar composites in an aqueous solution

There is a demand to develop techniques for the continuous removal/immobilization of heavy metals from contaminated soil and water bodies. In this study, a unique biochar preparation method was developed for the removal of cadmium. First, conventional biochars of corn straw were produced by pyrolysis at two temperatures and then treated using one-step synthesis at different ferric nitrate ratios and different calcination temperatures to produce magnetic biochars. Second, the prepared biochars were used as adsorbents for Cd(II) removal from a solution, and the best one was selected for further evaluation. Various techniques were used to characterize the adsorbents and determine the main adsorption mechanism. The results indicated that the biochars successfully carried iron particles within, which improved the specific surface area, formed inner-sphere complexes with oxygen-containing groups, and increased the number of oxygen-containing groups. The adsorption experiments revealed that MBC800-0.6₃₀₀ had a higher affinity for Cd(II) than the other adsorbents. Batch adsorption experiments were performed to explore the influence of the kinetics, isotherm, pH, thermodynamics, ionic strength, and humic acid on Cd(II) adsorption. The results indicated that the Langmuir model fit the Cd(II) adsorption best with MBC800-0.6₃₀₀ having the highest adsorption capacity (46.90 mg g^-1). The sorption kinetics of Cd(II) on the adsorbent follows a pseudo-second-order kinetics model. Because MBC800-0.6₃₀₀ is loaded with metal ions, it can be conveniently collected by a magnet. Thus, biochar modification methods with ferric nitrate impregnation provide an excellent approach to eliminating Cd(II) from aqueous solutions. The possible adsorption mechanisms include chemisorption, electrostatic interaction, and monolayer adsorption.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Efficient Removal of Cd(II) Using SiO2-Mg(OH)2 Nanocomposites Derived from Sepiolite

The pollution of Cadmium (Cd) species in natural water has attracted more and more attention due to its high cumulative toxicity. In the search for improved removal of cadmium from contaminated water, we characterized uptake on a recently identified nanomaterial (SiO₂-Mg(OH)₂) obtained by subjecting sepiolite to acid-base modification. The structural characteristics of SiO₂-Mg(OH)₂ were analyzed by means of SEM-EDS, Fourier Transform Infra-Red Spectroscopy (FTIR) and Powder X-ray Diffraction (PXRD). Static adsorption experiments were carried out to evaluate the effect of contact time, temperature, amount of adsorbent, and pH-value on the adsorption of Cd(II) by SiO₂-Mg(OH)₂. The results show that the pore structure of SiO₂-Mg(OH)₂ is well developed, with specific surface area, pore size and pore volume increased by 60.09%, 16.76%, and 43.59%, respectively, compared to natural sepiolite. After modification, the sepiolite substrate adsorbs Cd(II) following pseudo-second-order kinetics and a Langmuir surface adsorption model, suggesting both chemical and physical adsorption. At 298 K, the maximum saturated adsorption capacity fitted by Sips model of SiO₂-Mg(OH)₂ regarding Cd(II) is 121.23 mg/g. The results show that SiO₂-Mg(OH)₂ nanocomposite has efficient adsorption performance, which is expected to be a remediation agent for heavy metal cadmium polluted wastewater.

Manganese-modified biochar for highly efficient sorption of cadmium

In this study, corn stalk was modified by manganese (Mn) before (MBC₁) and after (MBC₂) pyrolysis at different temperatures (400~600 °C) under anaerobic conditions for Cd sorption in both water and soil. Batch experiments in aqueous solution were conducted to evaluate the optimum sorption capability by biochar with and without manganese-modified. Both types of manganese modification can improve the sorption capacity of Cd(II) on biochar, which is superior to the corresponding pristine biochar without modification, especially, pyrolyzed at 500 °C with 5:1 modification ratio. Under the optimal preparation conditions, the sorption percentage on MBC₂ was 11.01% higher than that of MBC₁. The maximum sorption capacity of MBC₂ was 191.94 mg g^-1 calculated by isotherm model. The performance of MBC₂ was also verified in soil stabilization experiments in Cd-contaminated soil. We can conclude from the results of BCR extraction that all the application rates of MBC₂ (1%, 2%, and 3%) can reduce the mild acid-soluble fraction Cd. The reducible, oxidizable, and residual fraction Cd showed an upward trend, thus controlling the migration, transformation, and enrichment of Cd in soil. The characteristic analysis showed biochar has more irregular fold and more particle-aggregated surface after modification. The main components of these aggregated particles are manganese oxides (MnO_x) with high sorption capacity, such as the MnO_x crystal structure loaded on MBC₂ is a mixed structure of δ-MnO₂ and MnO. However, these particles may block the biochar pores, or some of the pores may collapse at high temperatures during the modification process. The specific surface area was reduced, even if the sorption effect of MBC was strongly enhanced. Meanwhile, under the action of the secondary pyrolysis of MBC₂ modification process, the MBC₂ has a higher degree of aromatization with more potential active sorption sites for Cd. The study concluded that the MBC₂ could be a promising amendment for Cd in both water and soil real field applications.

Goethite-modified biochar restricts the mobility and transfer of cadmium in soil-rice system

Cadmium (Cd) contamination of paddy soils has raised serious concerns for food safety and security. Remediation and management of Cd contaminated soil with biochar (BC) and modified biochar is a cost-effective method and has gained due attention in recent years. Goethite-modified biochar (GB) can combine the beneficial effects of BC and iron (Fe) for remediation of Cd contaminated soil. We probed the impact of different BC and GB amendments on Cd mobility and transfer in the soil-rice system. Both BC and GB effectively reduced Cd mobility and availability in the rhizosphere and improved the key growth attributes of rice. Although BC supply to rice plants enhanced their performance in contaminated soil but application of 1.5% GB to the soil resulted in prominent improvements in physiological and biochemical attributes of rice plants grown in Cd contaminated soil. Sequential extraction results depicted that BC and GB differentially enhanced the conversion of exchangeable Cd fractions to non-exchangeable Cd fractions thus restricted the Cd mobility and transfer in soil. Furthermore, supplementing the soil with 1.5% GB incremented the formation of iron plaque (Fe plaque) and boosted the Cd sequestration by Fe plaque. Increase in shoot and root biomass of rice plants after GB treatments positively correlates with incremented chlorophyll contents and gas exchange attributes. Additionally, the oxidative stress damage in rice plants was comparatively reduced under GB application. These findings demonstrate that amending the soil with 1.5% GB can be a potential remediation method to minimize Cd accumulation in paddy rice and thereby can protect human beings from Cd exposure.

Modification of biochar with silicon by one-step sintering and understanding of adsorption mechanism on copper ions

Novel salt-based biochar was prepared by loading silicon (Si) on cornstalk biomass with "one-step sintering" technique. Manganese (Mn) was also used to modify biochar with the same method as a control. Surface morphology, elemental composition, crystal structure and surface area of "salt-based biochars" were analyzed by SEM + EDS, XRD, FTIR and BET, and the effects of the dosage of absorbent and pH of solution on the adsorption process were explored. Si and Mn could be successfully attached on the biochar surface as oxide forms. SiBC exhibited a dense and agglomerated surface, while MnBC was a kind of porous and rough materials. The optimal adsorption capability would realize when putting 2 g/L of biochar composites at pH = 5-6. Adsorption isotherms, adsorption kinetics, combine with FTIR and XPS were carried out to help to elaborate the adsorption mechanisms. The maximum adsorption capacity of Cu (II) was 152.61 mg/g on SiBC and it could reach at 97% of removal rate within 10 min when the concentration was 100 mg/L, while MnBC had to take 500 min to achieve the same adsorption effect, and reached 187.76 mg/g of maximum adsorption capacity. Langmuir model and pseudo-second-order model were more suitable for both SiBC and MnBC, which meant the monolayer and chemical adsorption were dominated. Surface complexation and precipitation was attributed to SiBC. Specialistic adsorption, ion exchange and intra-particle diffusion was put it down to MnBC.

Adsorption of divalent cadmium by calcified iron-embedded carbon beads

A novel iron-embedded carbon bead was prepared by the calcination of a calcium alginate gel bead mixed with iron nanoparticles coated by polydopamine. The prepared iron-embedded carbon bead was characterized by infrared spectrum analysis, X-ray diffraction, Raman spectroscopy, vibrating sample magnetometry, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. It was discovered that the novel structure efficaciously prevented the agglomeration of iron nanoparticles. Additionally, the effects of dose, pH, exposure time, temperature and initial concentration on the adsorption of Cd(ii) were studied, and the reusability of the material was analyzed. Fe/SA-C showed high Cd(ii) removal capability (220.3, 225.7, 240.8 mg g⁻¹ at 288, 298, 308 K), easy recoverability and high stability. In addition, some slightly different interpretations of the adsorption mechanism are given. This study clearly revealed that Fe/SA-C has potential application in the removal of Cd(ii).

The material structure could prevent Fe nanoparticle agglomeration during synthesis and maintain Fe stability during adsorption. Fe/SA-C had a superior adsorption property and easy recoverability.

Selective removal and persulfate catalytic decomposition of diethyl phthalate from contaminated water on modified MIL100 through surface molecular imprinting

Adsorptive removal of phthalate esters from wastewater combined with their persulfate (PS) catalytic degradation has attracted the attention of many researchers. In this study, the adsorptive and catalytic properties of an MIL100 material obtained by a green synthetic route have been optimized by a surface molecular imprinting technique. Results have shown that there are two steps in the molecular imprinting process. A polymerization is first carried out in the internal channels of the material and the imprinting layer is then formed on the surface. The relative proportions of the starting materials for the synthesis have been optimized through the design of a three-dimensional response surface. The amount of pollutant adsorbed was increased fourfold after surface imprinting, reaching 13.6 mg g^-1. The homogeneity of the recognition sites has been evaluated by dynamics calculations and the Freundlich equation. The selective adsorption ability of the material for diethyl phthalate was improved, and the process involved chemical adsorption. The catalytic properties of the material after imprinting were increased about 1.5-fold, indicating that selective adsorption is important. Such molecularly imprinted polymers may potentially serve as good functional materials for the removal of phthalate esters from wastewater.

Critical review of magnetic biosorbents: Their preparation, application, and regeneration for wastewater treatment

The utilisation of magnetic biosorbents (metal or metal nanoparticles impregnated onto biosorbents) has attracted increasing research attention due to their manipulable active sites, specific surface area, pore volume, pore size distribution, easy separation, and reusability that are suitable for remediation of heavy metal(loid)s and organic contaminants. The properties of magnetic biosorbents (MB) depend on the raw biomass, properties of metal nanoparticles, modification/synthesis methods, and process parameters which influence the performance of removal efficiency of organic and inorganic contaminants. There is a lack of information regarding the development of tailored materials for particular contaminants and the influence of specific characteristics. This review focuses on the synthesis/modification methods, application, and recycling of magnetic biosorbents. In particular, the mechanisms and the effect of sorbents properties on the adsorption capacity. Ion exchanges, electrostatic interaction, precipitation, and complexation are the dominant sorption mechanisms for ionic contaminants whereas hydrophobic interaction, interparticle diffusion, partition, and hydrogen bonding are the dominant adsorption mechanisms for removal of organic contaminants by magnetic biosorbents. In generally, low pyrolysis temperatures are suitable for ionic contaminants separation, whereas high pyrolysis temperatures are suitable for organic contaminants removal. Additionally, magnetic properties of the biosorbents are positively correlated with the pyrolysis temperatures. Metal-based functional groups of MB can contribute to an ion exchange reaction which influences the adsorption capacity of ionic contaminants and catalytic degradation of non-persistent organic contaminants. Metal modified biosorbents can enhance adsorption capacity of anionic contaminants significantly as metal nanoparticles are not occupying positively charged active sites of the biosorbents. Magnetic biosorbents are promising adsorbents in comparison with other adsorbents including commercially available activated carbon, and thermally and chemically modified biochar in terms of their removal capacity, rapid and easy magnetic separation which allow multiple reuse to minimize remediation cost of organic and inorganic contaminants from wastewater.

Synergistic immobilization of potentially toxic elements (PTEs) by biochar and nanoparticles in alkaline soil

Biochar and nanoparticle (NP) have the ability to sorb potentially toxic elements (PTEs) from soil and reduce toxicity and leaching into water bodies. However, there is need to tailor biochar formulations to soil types. In this study, we investigate the mobility and chemical forms of Cd, Cr, Cu, Ni, and Zn in a spiked, alkaline soil after amendment with combination of NPs (nano-Fe (NF), nano-clay (NC)) and biochars (almond shell 500 °C, walnut shell 400 °C) in different doses (0, 2.5, 5, and 10%). Many previous studies concluded biochar immobilized PTEs due to an increase in soil pH, which can be disregarded here (soil pH 7.9). In a twenty-week column leaching experiment biochar addition significantly decreased PTE leaching and NP addition further immobilized PTEs in most cases. On average almond biochar more effectively reduced Zn leaching and walnut biochar was more effective in decreasing the leaching of Cd, Cr, and Ni (e.g. 5% biochar reduced Cr leaching by 68%). Copper was immobilized effectively by both biochars. Nano-clay combined with walnut biochar performed best in all treatments, in particular for Cd, Ni, and Zn (e.g. 10% walnut biochar only and in combination with NC reduced Zn leaching by 14.2% and 58.5%, respectively). After amendment, PTEs were present in the Fe-Mn oxides, organic and residual fractions and less in the exchangeable fraction, reducing PTE availability and leachability. The results demonstrate that even for cationic PTEs that behave similarly in the environment optimal biochar-mineral formulations can differ.

Copper Adsorption by Magnetized Pine-Needle Biochar

The Cu(II) adsorption from aqueous solutions by magnetic biochar obtained from pine needles has been studied by means of batch-type experiments. The biochar fibers have been magnetized prior (pncm: carbonized-magnetized pine needles) and after oxidation (pncom: carbonized-oxidized-magnetized pine needles) and have been used as adsorbents to study the presence of carboxylic moieties on the magnetization and following adsorption process. The effect of pH (2–10), initial metal concentration (10−5–9·10−3 mol·L−1) and contact time (0–60 min) has been studied by varying the respective parameter, and the adsorbents have been characterized by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurements prior and after Cu(II)-adsorption. FTIR measurements were performed to investigate the formation of surface species and XRD measurements to record possible solid phase formation and characterize formed solids, including the evaluation of their average crystal size. The data obtained from the batch-type studies show that the oxidized magnetic biochar (pncom) presents significantly higher adsorption capacity (1.0 mmol g−1) compared to pncm (0.4 mmol g−1), which is ascribed to the synergistic effect of the carboxylic moieties present on the pncom surface, and the adsorption process follows the pseudo-second order kinetics. On the other hand, the FTIR spectra prove the formation of inner-sphere complexes and XRD diffractograms indicate Cu(II) solid phase formation at pH 6 and increased metal ion concentrations.

Chitosan-grafted tetrapolymer using two monomers: pH-responsive high-performance removals of Cu(II), Cd(II), Pb(II), dichromate, and biphosphate and analyses of adsorbed microstructures

For circumventing the cumbersome and expensive multifunctional and multipolymer adsorbents for high-performance removals of hazardous water-contaminant(s), chitosan-g-[2-acrylamido-2-methyl-1-propanoic acid (AMPS)-co-2-(3-acrylamidopropanamido)-2-methylpropane-1-sulfonic acid (APAMPS)-co-2-(N-(3-amino-3-oxopropyl)acrylamido)-2-methylpropane-1-sulfonic acid (NAOPAMPS)-co-acrylamide (AM)] (i.e., chitosan-g-tetrapolymer), a multifunctional scalable and reusable hydrogel, was synthesized by grafting of chitosan and in situ attachments of N-H functionalized NAOPAMPS and APAMPS hydrophilic acrylamido-monomers during free-radical solution-polymerization of the two ex situ added AMPS and AM monomers in water. The response surface methodology was employed to synthesize one hydrogel envisaging the optimum balance between swelling and stability for the superadsorption of Cu(II), Cd(II), Pb(II), Cr₂O₇^2-, and HPO₄^2-. The in situ attachments of NAOPAMPS and APAMPS, grafting of chitosan into tetrapolymer, structures and properties, pH-responsive abilities, superadsorption mechanism, and reusability were understood via in depth microstructural analyses of adsorbed and/or unadsorbed chitosan-g-tetrapolymer(s) through ¹H/¹³C NMR, FTIR, XPS, TGA, XRD, DLS, and pH_PZC. The maximum adsorption capacities of Cd(II), Cu(II), Pb(II), Cr₂O₇^2-, and HPO₄^2- were 1374.41, 1521.08, 1554.08, 47.76, and 32.76 mg g^-1, respectively.

Influence of Selective Conditions on Various Composite Sorbents for Enhanced Removal of Copper (II) Ions from Aqueous Environments

Numerous pollutants, including dyes, heavy metals, pesticides, and microorganisms, are found in wastewater and have great consequences when discharged onto natural freshwater sources. Heavy metals are predominantly reported in wastewater. Heavy metals are persistent, non-biodegradable and toxic, transforming from a less toxic form to more toxic forms in environmental media under favourable conditions. Among heavy metals, copper is dominantly found in wastewater effluent. In this review, the effects of high concentration of copper in plants and living tissues of both aquatic animals and humans are identified. The performance of different polymer adsorbents and the established optimum conditions to assess the resultant remediation effect as well as the amount of copper removed are presented. This procedure allows the establishment of a valid conclusion of reduced time and improved Cu (II) ion removal in association with recent nano-polymer adsorbents. Nano-polymer composites are therefore seen as good candidates for remediation of Cu ions while pH range 5-6 and room temperature were mostly reported for optimum performance. The optimum conditions reported can be applied for other metal remediation and development of potent novel adsorbents and process conditions.

Functionalized magnetic mesoporous silica/poly(m-aminothiophenol) nanocomposite for Hg(II) rapid uptake and high catalytic activity of spent Hg(II) adsorbent

Currently, magnetic mesoporous silica nanospheres have been employed widely as adsorbents due to their large surface area and easy recovery. Herein, the functionalized magnetic mesoporous silica/organic polymers nanocomposite (MMSP) was fabricated by the grafted poly(m-aminothiophenol) embedded the aminated magnetic mesoporous silica nanocomposite based on Fe₃O₄ magnetic core, which was shelled by mesoporous silica and further modified by (3-aminopropyl) triethoxysilane. The adsorption properties of as-developed MMSP were systematically explored by altering the experimental parameters. The results indicated that the adsorption capacity and removal percentage of the MMSP could reach 243.83 mg/g and 97.53% within only 10 min at pH 4.0, and the coexisting ions had no significant effect on the selective Hg(II) ions removal from aqueous solutions, meanwhile, the adsorbent recovered by a magnet still exhibited good adsorption performance after recycled 5 times. In addition, by analyzing experimental data, the adsorption process of Hg(II) ions belonged to spontaneous exothermic adsorption, and the possible adsorption mechanisms were proposed based on the pseudo-second-order model and Langmuir model. After adsorption study, the waste material adsorbed Hg(II) was developed as an efficient catalyst for transformation of phenylacetylene to acetophenone with yield of 97.06%. In this study, we designed an efficient and selective material for Hg(II) ions remove and provided a treatment of the post-adsorbed mercury adsorbent by converting the waste into an excellent catalyst, which reduced the economic and environmental impact from conventional adsorption techniques.

Adsorptive purification of heavy metal contaminated wastewater with sewage sludge derived carbon-supported Mg(II) composite

A rod-like SDBC-Mg(II) composite was synthesized and optimized in the conditions of 25% Mg(II) loading and 500 °C calcination temperature. As-prepared SDBC-25%Mg(II)-500 adsorbent attained equilibrium in 30 min, with an extraordinary capacity of 2931.76 mg g^-1 (Pb(II)) and 861.11 mg g^-1 (Cd(II)), revealing a promising adsorbent for the removal of such metals so far. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Redlich-Peterson model. Furthermore, SDBC-25%Mg(II)-500 has a high anti-interference and selectivity in the presence of competing ions/other environmental factors and, also effectively eliminates >99% of Pb²⁺, Cd²⁺, Ag⁺ and Cu²⁺ ions from pond water, lake water and tap water. The adsorption process demonstrated a synergetic adsorption mechanism comprised of ion exchange with Mg(II), coordination with surface and inner carboxylic or carbonyl functional groups and co-precipitations as metal silicates, which is responsible for its superb adsorption performance. Besides, surface carvings of Mg(II) and tunnels on the rods resulting from the sludge carbonization provided a high surface area (91.57 m² g^-1), extra sorption sites and room for easy pollutant diffusion which contributed to surface physical adsorption. Furthermore, this technique demonstrate an alternative pathway that will relieve the burdens of sewage sludge treatment process and turn this solid waste into highly efficient adsorbent for eliminating heavy metal ions from wastewater. This can be considered as a feasible waste resource utilization to meet with the requirement from both ecology and economy for auspicious applications in industries.

A comparative study on biochar properties and Cd adsorption behavior under effects of ageing processes of leaching, acidification and oxidation

Biochar has potential to control the bioavailability and migration of potentially toxic heavy metals in soil by adsorption. Natural ageing in the environment may change the physicochemical properties and adsorption function of biochar over the long-term. The present study compared the effects of different simulated ageing treatments on Cd adsorption of high and low temperature biochar from straw of corn (Zea mays). Fresh and aged biochars were systematically characterized by elemental analysis, FTIR, XPS, Zeta, SEM-EDS, XRD and the composition of their mineral ash. The adsorption of Cd to fresh and aged biochars was then assessed under the influence of pH. Drawing the results together the effects of ageing on the extent and mode of Cd adsorption could be elucidated. The results showed that the adsorption capacity of fresh biochar produced at 650 °C was higher than of biochar made at 350 °C, and that mineral co-precipitation plays a dominant role in Cd sorption. Leaching removed organic and inorganic ash components from biochars, markedly diminishing the capacity of the high temperature biochar to adsorb Cd. The adsorption performance of the low temperature biochar was dependent on surface complexation. The adsorption capacity of low-temperature biochar was markedly enhanced by oxygen-containing functional groups formed through acidification and oxidation. The long-term benefits of biochar in the management of polluted soil require a rethink, considering the contrasting ageing behavior of different temperature biochar and their response to different ageing environments.

Adsorption of cadmium and lead ions by phosphoric acid-modified biochar generated from chicken feather: Selective adsorption and influence of dissolved organic matter

To improve the adsorption efficiency, a H₃PO₄-modified biochar (CFCP) was prepared using chicken feather and applied to Cd²⁺ and Pb²⁺ adsorption. The pseudo-second-order model could explain the Cd²⁺ and Pb²⁺ adsorption behavior. CFCP had faster adsorption rate than non-modified biochar (CFC2). The Langmuir and Freundlich isotherm could better describe the Cd²⁺ and Pb²⁺ adsorption, respectively. The value of q_m for Cd²⁺ adsorption and K_F for Pb²⁺ adsorption by CFCP was 7.84 mg·g^-1 and 24.41 mg^1-(1/n)·L^1/n·g^-1, which was 1.38 and 5.41 times of the corresponding results of CFC2. Relative to Cd²⁺, Pb²⁺ was selectively adsorbed by biochars in the binary metal system. Phosphate precipitation explained in part the selective adsorption of Pb²⁺. Proline, glucose, and pH (4-6) had little influence on Cd²⁺ and Pb²⁺ adsorption. Electrostatic interaction, precipitation, and O-H bonds were the primary adsorption mechanisms. The increased N-containing heterocycles of CFCP accounted for the increased Cd²⁺ and Pb²⁺ adsorption.

Synthesis of a novel ternary HA/Fe-Mn oxides-loaded biochar composite and its application in cadmium(II) and arsenic(V) adsorption

Cadmium (Cd) and arsenic (As) are two of the most toxic elements. However, the chemical behaviors of these two elements are different, making it challenging to utilize a single adsorbent with high adsorption capacity for both Cd(II) and As(V) removal. To solve this problem, we synthesized HA/Fe-Mn oxides-loaded biochar (HFMB), a novel ternary material, to perform this task, wherein scanning electron microscopy (SEM) combined with EDS (SEM-EDS) was used to characterize its morphological and physicochemical properties. The maximum adsorption capacity of HFMB was 67.11 mg/g for Cd(II) and 35.59 mg/g for As(V), which is much higher compared to pristine biochar (11.06 mg/g, 0 mg/g for Cd(II) and As(V), respectively). The adsorption characteristics were investigated by adsorption kinetics and the effects of the ionic strength and pH of solutions. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) revealed that chelation and deposition were the adsorption mechanisms that bound Cd(II) to HFMB, while ligand exchange was the adsorption mechanism that bound As(V).

Removal of Cd(II) by modified maifanite coated with Mg-layered double hydroxides in constructed rapid infiltration systems

To improve the adsorption performance of Cd(II) by maifanite in constructed rapid infiltration systems (CRIS), Mg-layered double hydroxides (MgAl-LDHs, MgFe-LDHs) are prepared by a co-precipitation method and in-situ coated on the surface of original maifanite. Characterization of the successful LDHs-coating modification is realized by the following: scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Brunauer Emmett Teller (BET). In the purification experiments, the average removal rates of Cd(II) were 97.66% for maifanite/MgAl-LDHs and 97.54% for maifanite/MgFe-LDHs, approximately 11% greater than for the original maifanite. Isothermal adsorption experiments and adsorption kinetic experiments were conducted to explore the Cd(II) adsorption mechanism. The modified maifanite demonstrated a higher Langmuir adsorption capacity and stronger surface bond energies compared to the original maifanite. The adsorption type of Cd(II) by maifanite/Mg-LDHs and original maifanite was monolayer adsorption based mainly on chemical adsorption. Furthermore, the extracellular polymeric substances and dehydrogenase activities of the microorganisms were measured and analyzed to study the effect of microorganisms on the removal of Cd(II) in the test columns. High-throughput sequencing technology was also applied to analyze the composition and diversity of bacterial communities. Based on a simple estimation, the synthesis cost of maifanite/MgAl-LDHs was only ¥ 0.33/Kg. In brief, maifanite/Mg-LDHs is an efficient and economical substrate for a CRIS for Cd(II) removal.

A novel clean production approach to utilize crop waste residues as co-diet for mealworm (Tenebrio molitor) biomass production with biochar as byproduct for heavy metal removal

Proper management of waste crop residues has been an environmental concern for years. Yellow mealworms (larvae of Tenebrio molitor Linnaeus, 1758) are major insect protein source. In comparison with normal feed wheat bran (WB), we tested five common lignocellulose-rich crop residues as feedstock to rear mealworms, including wheat straw (WS), rice straw (RS), rice bran (RB), rice husk (RH), and corn straw (CS). We then used egested frass for the production of biochar in order to achieve clean production. Except for WS and RH, the crop residues supported mealworms' life activity and growth with consumption of the residues by 90% or higher and degraded lignin, hemicellulose and cellulose over 32 day period. The sequence of degradability of the feedstocks is RS > RB > CS > WS > RH. Egested frass was converted to biochar which was tested for metal removal including Pb(II), Cd(II), Cu(II), Zn(II), and Cr(VI). Biochar via pyrolysis at 600 °C from RS fed frass (FRSBC) showed the best adsorption performance. The adsorption isotherm fits the Langmuir model, and kinetic analysis fits the Pseudo-Second Order Reaction. The heavy metal adsorption process was well-described using the Intra-Particle Diffusion model. Complexation, cation exchange, precipitation, reduction, deposition, and chelation dominated the adsorption of the metals onto FRSBC. The results indicated that crop residues (WS, RS, RB, and CS) can be utilized as supplementary feedstock along with biochar generated from egested frass to rear mealworms and achieve clean production while generating high-quality bioadsorbent for environment remediation and soil conditioning.

Enhancement of cadmium removal by oxygen-doped carbon nitride with molybdenum and sulphur hybridization

Graphitic carbon nitride, as a popular material in the field of environmental remediation, still suffers from unsatisfactory performance for heavy metals adsorption owing to lack of specific adsorption sites. In this study, molybdenum (Mo) and sulphur (S) were simultaneously introduced onto the surface of oxygen-doped graphitic carbon nitride (OCN) for the enhancement of Cd²⁺ adsorption. The synthesized MOS/OCN-1 exhibited substantially increased maximum adsorption capacity of 293.8 mg/g, calculated from Sips isotherm model, which was 8.7 times higher than that for pristine OCN (33.9 mg/g). The adsorption efficiency of MOS/OCN-1 was >94% even under high concentration of coexisting ions (i.e., Ca²⁺, Mg²⁺ and Zn²⁺). MoO₃ and MoS₂ on the surface of OCN were proven to interact with Cd²⁺ by forming CdMoO₄ and CdS species. OCN provided a stable matrix with a large surface area making more active sites exposed, which greatly facilitated Mo(IV) oxidation and Cd²⁺ precipitation. Our findings revealed that as well as the well-known Cd-S interaction, Mo atoms in the hybrid composites also played an important role in Cd²⁺ removal, which opened up the application possibility of OCN with Mo and S hybridization for in-situ Cd²⁺ remediation.

Effect of oxidation-induced aging on the adsorption and co-adsorption of tetracycline and Cu2+ onto biochar

The bamboo biochars pyrolyzed at 400 °C and 600 °C (BC400 and BC600) were modified by hydrogen peroxide (H₂O₂) to obtain the oxidized biochars. Biochar stability and the effect of oxidation treatment on the adsorption and co-adsorption of tetracycline (TC) and Cu²⁺ onto biochars were investigated. The calculated carbon loss of biochars after oxidation treatment indicated that BC600 presented higher carbon stability than BC400 due to the condensed aromatic structure of biochar. Moreover, oxidation treatment introduced O-containing functional groups on biochar surface, but destructed the aromatic structures of oxidized biochars, which in turn affected the adsorption capacity of biochars for TC and Cu²⁺. Oxidation treatment obviously enhanced the adsorption of TC and Cu²⁺ onto BC400 owing to the increase of O-containing functional groups, but significantly decreased TC and Cu²⁺ adsorption onto BC600 because of the decreased π-π dispersive forces between biochar and adsorbate. The promotion effect of Cu²⁺ on TC adsorption onto BC400 changed into inhibition effect after chemical oxidation owing to the pore blockage. However, the promotion degree of Cu²⁺ for TC adsorption onto BC600 was enhanced through oxidation treatment due to electrostatic attraction and complexation. Meanwhile, oxidation treatment reduced the inhibition degrees of TC for Cu²⁺ adsorption onto biochars, which was attributed to the increased amount of electron-rich groups. The results are helpful for the application of biochars in the soils remediation.

Sustainable valorization of mesoporous aluminosilicate composite from display panel glasses waste for adsorption of heavy metal ions

The recycling of the huge amount of thin film transistor liquid crystal display (TFT-LCD) glass wastes has become one of the worldwide environmental issues. Herein, a novel and cost-effective synthesis method for the fabrication of mesoporous aluminosilicate composite (M-ANC) from the TFT-LCD waste has been developed to serve as the environmentally benign adsorbent for the removal of metal ions including Cu²⁺, Zn²⁺ and Ni²⁺. After melting at 1000 °C in the presence of Na₂CO₃ for phase separation, nanoparticles with average particle size of 12 nm appear on the surface of M-ANC, and subsequently results in the production of mesoporous structure with a surface area of 175 m² g^-1. The tailored M-ANC shows negatively charged and functional groups, which exhibits an excellent adsorption capacity toward metal ion removal in the pH range of 1.5-7.0. The maximum Langmuir adsorption capacity of Cu²⁺, Zn²⁺ and Ni²⁺ are determined to be 64.5, 34.0 and 23.1 mg g^-1, respectively, at pH 3.5. Moreover, the environmental applicability of M-ANC is evaluated by column experiment in the presence of real electroplating wastewater. M-ANC can effectively remove Ni²⁺ in the electroplating wastewater with the adsorption capacity of 18.7 mg g^-1. Results obtained in this study clearly indicate that M-ANC recycled from TFT-LCD is a novel environmentally friendly adsorbent toward metal ion removal, which can open a gateway to fabricate mesoporous aluminosilicate materials through the recycling of other electronic wastes for real environmental application to remove metal ions and other emerging pollutants in the contaminated water and wastewater.

The effects of interaction between vermiculite and manganese dioxide on the environmental geochemical process of thallium

The interaction among various soil minerals can significantly impact on the environmental geochemical process of contaminants. Therefore, this study investigated the effects of interaction between vermiculite (VER) and manganese dioxide (MnO₂) on the migration and transformation of Tl(I). The VER exhibited typical layered structure and MnO₂ possessed a flower-like structure with serious reunion phenomenon, while the production of interaction between vermiculite and manganese dioxide, labeled VER-MnO₂, illustrated as fish scales evenly spread over a large sheet, suggesting that MnO₂ could triumphantly be anchored on the VER and the aggregation of MnO₂ was prevented. Compared with the pure MnO₂, VER acted as template substrate contributed the higher specific surface area (298.18 m²·g^-1) and the oxidation degree of Mn. VER-MnO₂ showed the highest fixation capacity (144.29 mg·g^-1) than other two materials in the order VER-MnO₂ > MnO₂ > VER, and there was no risk derived from Mn dissolution. The influence mechanism of VER-MnO₂ on Tl(I) migration and transformation lied in immobilization, ion exchange and oxidization. Fixed-bed column immobilization experiments showed that VER-MnO₂ could purify drinking water contaminated by Tl (20 μg·L^-1) and the effective breakthrough volumes were 900 bed volumes until reaching the maximum limits allowed in drinking water (0.1 μg·L^-1). VER-MnO₂ excellently catches Tl to prevent groundwater pollution. This study provides a theoretical guidance for environmental fate and restoration of soil heavy metal pollution.

Mechanisms and reutilization of modified biochar used for removal of heavy metals from wastewater: A review

Heavy metals (HMs) pose serious threat to both human and environmental health and therefore, effective and low-cost techniques to remove HMs are urgently required. Because HMs are difficult to be biodegraded and transformed, adsorption is a most promising treatment method in recent times. Biochar (BC), a low-cost and sustainable adsorbent material, has recently attracted much research attention due to its broad application prospects. While BC has many merits, it has a lower HMs adsorption efficiency than traditional activated carbon, limiting its practical applications. Furthermore, the HMs retained by BC are difficult to be desorbed, making the used sorbent material hazardous wastes if not well disposed of under natural conditions. Therefore, it is critical to seek effective surface modifications for BC, to improve its ability to HMs removal ability and the recyclability of BC loaded with HMs. This review represents and evaluates the reported modification methods for BC, the corresponding HMs removal mechanisms and the potential for reutilization of BC loaded with HMs. This review provides a basis for the effective practical application of BC in the treatment of HMs containing wastewater.

Adsorption, recovery, and regeneration of Cd by magnetic phosphate nanoparticles

Adsorption plays an important role in removing cadmium (Cd²⁺) from water, and magnetic adsorbents are increasingly being used due to their ease of separation and recovery. Magnetic Fe₃O₄-coated hydroxyapatite (HAP) nanoparticles (nHAP-Fe₃O₄) were developed by co-precipitation and then used for the removal of Cd²⁺ from water. The properties of these nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and magnetization curves. Experiments were conducted to investigate the effects of adsorption and mechanisms. Results illustrated that kinetic data were well fitted by a pseudo-second-order model. The adsorption capacity of nHAP-Fe₃O₄ was 62.14 mg/g. The mechanisms for the adsorption of Cd²⁺ on nHAP-Fe₃O₄ included rapid surface adsorption, intraparticle diffusion, and internal particle bonding, with the ion exchange with Ca²⁺ and chemical complexation being the most dominant. The regeneration efficiency and recovery rate of nHAP-Fe₃O₄ eluted by EDTA-Na₂ after the fifth cycle were 63.04% and 40.2%, respectively. Results revealed that the feasibility of nHAP-Fe₃O₄ as an adsorbent of Cd²⁺ and its environmental friendliness make it an ideal focus for future research.

Manganese Oxide Nanochips as a Novel Electrocatalyst for Direct Redox Sensing of Hexavalent Chromium

In order to maintain a healthy organisation of bionetworks, both qualitative and quantitative estimation of hexavalent chromium in food and beverage samples is required based on proper quality control and assurance. Nonetheless, conventional quantitation techniques for hexavalent chromium generally suffer from certain limitations (e.g., the need for expertise, costly equipment, and a complicated procedure). This research was performed to elaborate a novel method to quantify hexavalent chromium based on an electrochemical cyclic voltammetry technique. To this end, nanochips of manganese oxide (Mn₃O₄: approximately 80–90 nm diameter and 10 nm thickness) were synthesized using a chemical method and characterized with spectroscopic and microscopic approaches. These nanochips were employed as proficient electrocatalytic materials in direct redox sensing of hexavalent chromium in both real samples and laboratory samples. Manganese oxide nanochips felicitated large surface area and catalytic action for direct electrochemical reduction of hexavalent chromium at electrode surface. This fabricated nanochip sensor presented a detection limit of 9.5 ppb with a linear range of 50–400 ppb (sensitivity of 25.88 µA cm⁻² ppb⁻¹).

Highly efficient removal of Cr(VI) and Cu(II) by biochar derived from Artemisia argyi stem

In this work, a novel biochar was prepared from the Artemisia argyi stem at 300 °C (AS300), 450 °C (AS450), and 600 °C (AS600). The structural properties of these biochars were characterized with various tools. The sorption kinetic processes of Cr(VI) and Cu(II) onto these biochars were better described by the pseudo-second order. The sorption isotherm processes of Cr(VI) onto these biochars were better described by the Freundlich model while the adsorption processes of Cu(II) were consistent with the Langmuir model. Batch sorption experiments showed that AS600 had the maximum adsorption capacity to Cr(VI) and Cu(II) with 161.92 and 155.96 mg/g, respectively. AS600 was selected for the follow-up batch and dynamic adsorption experiments. Results showed that AS600 had larger adsorption capacity for Cr(VI) at lower pH while the larger adsorption capacity for Cu(II) was found at higher pH. The effect of ionic strength on the adsorption of Cu(II) by AS600 was greater than that on the adsorption of Cr(VI). Dynamic adsorption experiments showed that Cu(II) had a higher affinity for the adsorption sites on the AS600 compared with Cr(VI). The adsorption mechanisms mainly involved electrostatic attraction, ion exchange, pore filling, and chemical bonding effect. Graphical abstract.

Enhanced trifluoroacetate removal from groundwater by quaternary nitrogen-grafted granular activated carbon

This research reports an integrated method for synthesizing a quaternary nitrogen-grafted activated carbon that is derived from a subbituminous coal source. The protocol employed nitric acid oxidation, thermal ammonia treatment and methyl iodide quaternization. The quaternized product greatly increased trifluoroacetate (TFA, CF₃COO^-) removal from a groundwater source. This quaternary nitrogen-grafted carbon (designated AWNQ) exhibited the highest TFA adsorption capacity of 32.9 mg/g and exhibited high energy of adsorption for TFA. Also, when processing groundwater that had been spiked with 200 ppb TFA, this quaternary nitrogen-grafted carbon removed TFA to 3 ppb breakthrough for 1860 BV, which was twelve times longer than the 150 BV for the pristine carbon. The enhanced sorption was attributed to its high quaternary nitrogen ratio (1.30, at.%), which offered 0.69 meq/g positive charge. Furthermore, high regeneration efficiency (89.5%) was achieved by the proposed regeneration protocol. The mixed regenerant (ethanol and NaCl solution) effectively stripped off the loaded TFA and regenerated the quaternary nitrogen sites. This quaternary nitrogen-grafted carbon with its fast and high uptake capacity offered technical promise for TFA removal from groundwater.

Non-competitive and competitive adsorption of Cd2+, Ni2+, and Cu2+ by biogenic vaterite

Ubiquitous bio-minerals exert significant effects on the migration and transformation of metal ions in the environment, however, research into the adsorption of heavy metals by biogenic vaterite (BV) has rarely been reported. The aim of our research was to evaluate the removal effects of Cd²⁺, Ni²⁺, and Cu²⁺ in single and multi-metal ion aqueous solutions using BV induced by Bacillus subtilis. The results demonstrate that the adsorption data of BV for metal ions are more accurately fitted to the Langmuir model compared with the Freundlich model. The max adsorption capacity (mg/g) order of BV was Ni (270.27) > Cu (178.57) > Cd (172.41) in a single-metal system, and Cu (175.44) > Ni (94.34) > Cd (30.30) in a multi-metal system (pH = 5.0, 2.5 g/L). A competitive effect exists amongst heavy metals in multi-metal ion systems, and Cu²⁺ adsorption is less affected by other two ions. Furthermore, BV can maintain favourable adsorption characteristics even in a very strong acidic environment (pH = 3.0), and its adsorptive capability becomes more favourable at higher temperatures. Kinetic analysis shows that the adsorption process can be better described by a pseudo-second-order model. XRD, FTIR, and SEM-EDS results reveal that metal ion adsorption on BV mostly happened through physical means, and the favourable adsorption characteristics of BV might be attributable to its larger specific surface area, aggregated spherical polyporous and organic-inorganic structure.

Synthesis and adsorption of FeMnLa-impregnated biochar composite as an adsorbent for As(III) removal from aqueous solutions

Groundwater with elevated As concentrations is a global concern, and low-cost, high-efficiency removal technologies are necessary. Therefore, we have prepared three adsorbent FeMnLa-impregnated biochar composites (FMLBCs) for the efficient removal of As(III) from aqueous solutions and characterized them using a variety of techniques. We found that the efficiency of As(III) removal increased with increasing La content and that the removal mainly occurred via adsorption and oxidation. Moreover, the removal of As(III) by FMLBCs was rapid and was best fitted to a pseudo-second-order kinetic model. The adsorption isotherms were well described by the Langmuir equation, and the maximum As(III) adsorption capacity was 15.34 mg g^-1. These results highlight the significant potential of FMLBCs as adsorbents for As(III) removal from aqueous solutions.

Adsorption of Cd(II) from aqueous solution by Pennisetum sp. straw biochars derived from different modification methods

The adsorption mechanism of Cd (II) was investigated by Pennisetum sp. straw biochars (JBC) that were modified by two different methods: KMnO₄ impregnation (JMB1) and H₂O₂ impregnation (JMB2). A scanning electron microscope and energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), a Fourier transform infrared spectrometer (FTIR), and a Brunauer-Emmett-Teller (BET) specific surface area analysis were employed to examine the physicochemical characteristics of biochars. The Cd(II) adsorption kinetic fit, the Langmuir model well, and the maximum adsorption capacity occurred in the following order: JMB1 (90.32 mg/g) > JMB2 (45.18 mg/g) > JBC (41.79 mg/g), suggesting that JMB1 had an excellent adsorption performance. Finally, X-ray photoelectron spectroscopy (XPS) was used to explore the main adsorption mechanism. Our results showed that JMB1 was an excellent adsorbent in removing Cd(II) from aqueous solution.

Nanomaterials as versatile adsorbents for heavy metal ions in water: a review

Over the years, heavy metal pollution has become a very serious environmental problem worldwide. Even though anthropogenic sources are believed to be the major cause of heavy metal pollution, they can also be introduced into the environment from natural geogenic sources. Heavy metals, because of their toxicity and carcinogenicity, are considered to be the most harmful contaminants of groundwater as well as surface water, a serious threat to both human and aquatic life. Nanomaterials due to their size and higher surface area to volume ratio show some unique properties compared to their bulk counterpart and have drawn significant attention of the scientific community in the last few decades. This large surface area can make these materials as effective adsorbents in pollution remediation studies. In this review, an attempt has been made to focus on the applicability of different types of nanomaterials, such as clay-nanocomposites, metal oxide-based nanomaterials, carbon nanotubes, and various polymeric nanocomposites as adsorbents for removal of variety of heavy metals, such as As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, U, V, and Zn, from water as reported during the last few years. This work tries to analyze the metal-nanomaterial interactions, the mechanism of adsorption, the adsorption capacities of the nanomaterials, and the kinetics of adsorption under various experimental conditions. The review brings forward the relation between the physicochemical properties of the nanomaterials and heavy metal adsorption on them.

Biomass facilitated phase transformation of natural hematite at high temperatures and sorption of Cd2+ and Cu2

Phase changes of natural hematite are often practiced to improve heavy metal removal and magnetism for easy recycling. In this work, pinewood biomass (PB) and natural hematite (H) admixtures were pyrolyzed at 300, 450 and 600 °C under N₂ environment to prepare HBC nanocomposites (HBC300, HBC450 and HBC600). The X-ray diffraction (XRD) confirmed the reductive transformation of hematite (crystallite size ≈ 47 nm) into magnetite (25 nm) and further to wustite (25 nm) and zerovalent iron (48 nm). The Langmuir isotherms showed that the maximum sorption capacities of HBC300, HBC450, and HBC600 were 173, 138, and 130 mmol kg^-1 for Cd²⁺, and 359, 172, and 197 mmol kg^-1 for Cu²⁺, respectively. The higher pH up to 5 increased sorption of both Cd²⁺ and Cu²⁺, whereas the higher ionic strength (0.05-0.4 M) decreased Cd²⁺ sorption. Sorption of Cd²⁺ and Cu²⁺ by HBC300 was accompanied by one order of magnitude greater cation release than HBC450 and HBC600. In a binary system, Cd²⁺ sorption was depressed by over four times in presence of Cu²⁺. Overall, ion exchange was more pronounced for HBC300, and Cu²⁺ was more favorably retained by specific sorption than Cd²⁺. The greater magnetism of HBC nanoparticles favors separation from aqueous solutions.

Magnetic nanoferromanganese oxides modified biochar derived from pine sawdust for adsorption of tetracycline hydrochloride

In this study, a new type of composite material, namely modified biochar (MBC), was synthesized by loading the magnetic ferromanganese oxide nanoparticles on pine biochar. BET, SEM, and FTIR were employed to analyze the surface properties and pore structures of MBC. In addition, XRD was adopted to examine the crystal structure of MBC. Characterization results showed that the surface area and porosity of MBC have been greatly improved, and the functional groups have been introduced by ferromanganese oxides. Adsorption experiments of tetracycline hydrochloride (TC) including kinetics, isotherms, thermodynamics as well as the influence of pH, salt ion strength, and the environmental risk of MBC, were evaluated. The results revealed that the experimental data conformed to the pseudo-second-order kinetic model and the Freundlich isotherm model. In the adsorption process, MBC showed excellent adsorption ability (maximum capacity for TC 100.74 mg g^-1) to BC (33.76 mg g^-1). In isotherm experiments, the maximum adsorption capacity of TC by MBC reached 177.71 mg g^-1. Toxicity studies showed that the MBC had no harm to the environment. To conclude, MBC has great potential for applications in removing TC from water.

Characteristic of adsorption cadmium of red soil amended with a ferromanganese oxide-biochar composite

The increasing scarcity of arable land necessitates the development of effective decontamination techniques to re-gain contaminated areas and make them suitable for agricultural and other activities. Herein, we prepare a ferromanganese binary oxide-biochar composite (FMBC) and compare its potential for remediating Cd-contaminated red soil with that of biochar (BC), showing that (i) the obtained adsorption data are well described by the Langmuir model and (ii) Cd adsorption capacity increases with increasing adsorbent dosage. Specifically, the Cd adsorption capacity of FMBC-amended soil (6.72 mg g^-1) is demonstrated to significantly exceed that of BC-amended red soil (4.85 mg g^-1) and that of the control (2.28 mg g^-1) and increases with increasing temperature and pH, while the results of instrumental analyses indicate that Cd sorption on the soil surface occurs via the formation of CdO and Cd(OH)₂. Thus, FMBCs are concluded to play an important role in the adsorption of Cd, having the potential to prevent red soil acidification and improve soil quality, and are found to be promising remediation materials for mitigating the risks posed by Cd-contaminated red soil.