Implications of layered double hydroxides assembled biochar composite in adsorptive removal of contaminants: Current status and future perspectives

Multifunctional Sites for Enhanced Adsorption of Arsenic Using Sulfydryl-Modified Biochar/MgFe-Layered Double Hydroxides

Arsenic contamination in water poses a significant threat to the environment and human health due to the high toxicity of arsenic. Therefore, the development of functionalized materials with an enhanced adsorption capacity for arsenic remains a key research focus in water purification. In this study, straw powder was hydrothermally pretreated and subsequently pyrolyzed with zinc chloride at 700 °C to produce hydrothermal biochar with tailored pores. The hydrothermal biochar was then modified with sulfhydryl groups, and Sulfhydryl-Modified Biochar/MgFe-Layered Double Hydroxides (SH@HB/MgFe-LDH) composites were synthesized using the coprecipitation method. By utilizing HB with a high surface area, a composite material with a high specific surface area of 479.3677 m2/g was prepared. The experimental results indicated that the SH@HB/MgFe-LDH composites exhibited excellent arsenic adsorption performance across a wide pH range, achieving an arsenic adsorption capacity as high as 388.01 mg/g. The adsorption process and mechanism of the SH@HB/MgFe-LDH composites were investigated through adsorption kinetics, adsorption isotherms, thermodynamic analysis, and X-ray photoelectron spectroscopy. Additionally, recycling studies demonstrated that the composites maintained stable performance over three reuse cycles, showing good potential for practical applications. Overall, the SH@HB/MgFe-LDH composites offer an effective solution for arsenic pollution control in water while promoting the high-value utilization of agricultural and forestry waste.

Layered triple hydroxide (NiCoFe-LTH) with g-C3N4 hybrid nanocomposite as an adsorbent for Pb(II) extraction

Hybrid graphitic carbon nitride (g-C3N4) with layer triple hydroxide (LTH) nanocomposite synthesized using the hydrothermal procedure has been investigated as a novel adsorbent g-C3N4@NiCoFe-LTH in the dispersive solid phase microextraction (DSp-ME) for Pb(II) determination in the food and water samples. The nanocomposite was characterized using FTIR, SEM, SEM-EDX, and XRD techniques. Several analytical parameters were adjusted, including pH, adsorbent quantity, adsorption and elution time, sample and eluent volume, and elution solvent concentration, and found as 8.0, 7.5 mg, 60, and 30 s, 40 mL, 2 mL, and 0.5 mol/L, respectively. The method's accuracy was also evaluated using matrix effects. The results indicated the LOD as 0.163 μg/L, LOQ as 0.54 μg/L, and PF as 20. The percent relative standard deviation (%RSD) < 10 %, and the coefficient of determination (R2) was 0.999, demonstrating excellent precision and linearity. The method's effectiveness was also validated by analyzing certified reference materials (CRMs).

Synthesis of magnetic chitosan-composite biochar and its removal of copper ions (Cu2+) and methylene blue (MB) dye from aqueous solutions

This study presents the synthesis and evaluation of a magnetic chitosan-modified biochar (M-BC-CS) composite, developed from waste maize straw, for the efficient removal of copper ions (Cu2+) and methylene blue (MB) dye from aqueous solutions. The composite was characterized using advanced techniques such as SEM, BET, FTIR, XPS, and XRD, confirming its enhanced surface area, porosity, and magnetic properties. The study is aimed at investigating the optimal conditions for adsorption of Cu2+ and MB by M-BC-CS through analysis of the influence of diverse adsorbent dosages, pH levels, reaction times, and initial solution concentrations. The findings demonstrated that the equilibrium duration for the adsorption of Cu2+ and MB by M-BC-CS was 60 min, resulting in corresponding equilibrium adsorption quantities of 54.42 mg/g and 67.23 mg/g, respectively. To elucidate the adsorption mechanism, the present investigation applied the pseudo-second-order kinetic model and the Langmuir isotherm. The outcomes suggested that the adsorption process is attributable to single molecular layer chemisorption. XPS and FTIR analysis determined that ion exchange and electrostatic interactions are the predominant mechanisms responsible for the simultaneous adsorption of Cu2+ and MB, and a competitive relationship exists between these mechanisms. In addition, M-BC-CS exhibited exceptional magnetic separation performance, enabling effortless and effective separation when exposed to an external magnetic field. Furthermore, the results demonstrated that M-BC-CS has good reusability and high adsorption capacity also in real wastewater, thus emphasizing its potential as a promising adsorbent for the elimination of Cu2+ and MB from aqueous solutions.

Innovative recovery of matrix layered double hydroxide from simulated acid mine wastewater for the removal of copper and cadmium from wastewater

This study innovatively added biochar to optimize regulation in the neutralization process of simulated acid mine drainage (AMD) and recovered a new type of matrix layered double hydroxides (MLDH), which can be used to remove copper (Cu(II)) and cadmium (Cd(II)) from wastewater. A series of batch experiments show that MLDH with strong selective removal ability of Cu(II) and Cd(II) can be successfully obtained by adding biochar (BC) at pH = 5 end in the neutralization process. Kinetic and isotherm modeling studies indicated that the removal of Cu(II) and Cd(II) by the MLDH was a chemical multilayer adsorption process. The removal mechanism of Cu(II) and Cd(II) was further analyzed through related characterization analysis with contribution rate calculation: the removal rates of Cu(II) and Cd(II) by ion exchange were 42.7% and 26%, while that by precipitation were 34.5% and 49.9%, respectively. This study can provide a theoretical reference and experimental basis for the recovery and utilization of valuable by-products in AMD and the treatment of heavy metal wastewater.

Preparation and characterization of a novel nanocomposite based on MnCr-layered double oxide and CoFe2O4 spinel ferrite for methyl orange adsorption

Herein, the adsorption of methyl orange (MO), a dangerous anionic dye, from an aqueous solution was investigated using a novel magnetic nanocomposite adsorbent. A nanocomposite entitled manganese chromium-layered double oxide/cobalt spinel ferrite, (MnCr)-LDO5wt.%/CoFe2O4, which links the interlayer structural characteristics of layered double oxides (LDOs) with the magnetic properties of spinel ferrites (SFs) was synthesized using the eco-friendly co-precipitation technique. Determination of structural parameters, crystallite size, and micro-strain was done using X-ray diffraction (XRD) analysis. Transmission electron microscopy (TEM) was used to determine grain shape and size. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) to identify elements and oxidation states present in the prepared nanocomposite. Vibrating sample magnetometer (VSM) was utilized to examine the magnetic characteristic. A comprehensive comparative study about the effectiveness and durability of CoFe2O4 and (MnCr)5wt.%/CoFe2O4 as nanoadsorbents for MO was conducted. Numerous variables, including contact time, MO concentration, adsorbent dosage, and pH were tested for their effects on the adsorption removal percentages. The findings showed that the maximum removal percentage was 86.1% for 25 ppm of MO was for 0.1 g/100 mL of (MnCr)-LDO5wt.%/CoFe2O4 at pH = 3. Investigations of isotherms and kinetics were conducted under batch conditions. The Langmuir isotherm matched the experimental data, for both nanoadsorbents, quite well due to the homogeneous distribution of active sites. Adsorption kinetics data were found to be compatible with intra-particle diffusion and pseudo-second order models for CoFe2O4 and (MnCr)5wt.%/CoFe2O4, respectively. A total of five adsorption-desorption cycles were performed to determine the prepared adsorbents' recyclable nature.

MgO-mediated activation of active carbon as an affordable strategy to "in situ" degradation of lindane in contaminated soils

The accumulation in soil landfills of toxic and persistent lindane, widely used as an insecticide, triggers the risk of leaching with the concomitant contamination of surrounding rivers. Thus, viable remediation to eliminate in situ high concentrations of lindane in soil and water becomes an urgent demand. In this line, a simple and cost-effective composite is proposed, including the use of industrial wastes. It includes reductive and non-reductive base-catalyzed strategies to remove lindane in the media. A mixture of magnesium oxide (MgO) and activated carbon (AC) was selected for that purpose. The use of MgO provides a basic pH. In addition, the specific selected MgO forms double-layered hydroxides in water which permits the total adsorption of the main heavy metals in contaminated soils. AC provides adsorption microsites to hold the lindane and a reductive atmosphere that was increased when combined with the MgO. These properties trigger highly efficient remediation of the composite. It permits a complete elimination of lindane in the solution. In soils doped with lindane and heavy metals, it produces a rapid, complete, and stable elimination of lindane and immobilization of the metals. Finally, the composite tested in lindane-highly contaminated soils permits the "in situ" degradation of nearly 70% of the initial lindane. The proposed strategy opens a promising way to face this environmental issue with a simple, cost-effective composite to degrade lindane and fix heavy metals in contaminated soils.

Biochar/layered double hydroxides composites as catalysts for treatment of organic wastewater by advanced oxidation processes: A review

Heterogeneous advanced oxidation process has been widely studied as an effective method for removing organic pollutants in wastewater, but the development of efficient catalysts is still challenging. This review summaries the present status of researches on biochar/layered double hydroxides composites (BLDHCs) as catalysts for treatment of organic wastewater. The synthesis methods of layered double hydroxides, the characterizations of BLDHCs, the impacts of process factors influencing catalytic performance, and research advances in various advanced oxidation processes are discussed in this work. The integration of layered double hydroxides and biochar provides synthetic effects for improving pollutant removal. The enhanced pollutant degradation in heterogeneous Fenton, sulfate radical-based, sono-assisted, and photo-assisted processes using BLDHCs have been verified. Pollutant degradation in heterogeneous advanced oxidation processes using BLDHCs is influenced by process factors such as catalyst dosage, oxidant addition, solution pH, reaction time, temperature, and co-existing substances. BLDHCs are promising catalysts due to the unique features including easy preparation, distinct structure, adjustable metal ions, and high stability. Currently, catalytic degradation of organic pollutants using BLDHCs is still in its infancy. More researches should be conducted on the controllable synthesis of BLDHCs, the in-depth understanding of catalytic mechanism, the improvement of catalytic performance, and large-scale application of treating real wastewater.

Performance and Mechanism of Functionalized Water Hyacinth Biochar for Adsorption and Removal of Benzotriazole and Lead in Water

In this paper, water hyacinth is used to prepare biochar (WBC). A biochar-aluminum-zinc-layered double hydroxide composite functional material (WL) is synthesized via a simple co-precipitation method which is used to adsorb and remove benzotriazole (BTA) and lead (Pb²⁺) in an aqueous solution. In particular, this research paper uses various characterization methods to analyze WL and to explore the adsorption performance and adsorption mechanism of WL on BTA and Pb²⁺ in an aqueous solution through batch adsorption experiments combined with model fitting and spectroscopy techniques. The results indicate that the surface of WL contains a thick sheet-like structure with many wrinkles which would provide many adsorption sites for pollutants. At room temperature (25 °C), the maximum adsorption capacities of WL on BTA and Pb²⁺ are 248.44 mg·g^-1 and 227.13 mg·g^-1, respectively. In a binary system, during the process of using WL to adsorb BTA and Pb²⁺, compared with that in the absorption on Pb²⁺, WL shows a stronger affinity in the adsorption on BTA, and BTA would thus be preferred in the absorption process. The adsorption process of WL on BTA and Pb²⁺ is spontaneous and is endothermic monolayer chemisorption. In addition, the adsorption of WL on BTA and Pb²⁺ involves many mechanisms, but the main adsorption mechanisms are different. Among them, hydrogen bonding dominates the adsorption on BTA, while functional groups (C-O and C=O) complexation dominates the adsorption on Pb²⁺. When WL adsorbs BTA and Pb²⁺, the coexistence of cations (K⁺, Na⁺, and Ca²⁺) has a strong anti-interference ability, and WL can use a lower concentration of fulvic acid (FA) (<20 mg·L^-1) to improve its adsorption performance. Last but not least, WL has a stable regenerative performance in a one-component system and a binary system, which indicates that WL has excellent potential for the remediation of BTA and Pb²⁺ in water.

Global distribution of pesticides in freshwater resources and their remediation approaches

The role of pesticides in enhancing global agricultural production is magnificent. However, their unmanaged use threatens water resources and individual health. A significant pesticide concentration leaches to groundwater or reaches surface waters through runoff. Water contaminated with pesticides may cause acute or chronic toxicity to impacted populations and exert adverse environmental effects. It necessitates the monitoring and removing pesticides from water resources as prime global concerns. This work reviewed the global occurrences of pesticides in potable water and discussed the conventional and advanced technologies for the removal of pesticides. The concentration of pesticides highly varies in freshwater resources across the globe. The highest concentration of α-HCH (6.538 μg/L, at Yucatan, Mexico), lindane (6.08 μg/L at Chilka lake, Odisha, India), 2,4, DDT (0.90 μg/L, at Akkar, Lebanon), chlorpyrifos (9.1 μg/L, at Kota, Rajasthan, India), malathion (5.3 μg/L, at Kota, Rajasthan, India), atrazine (28.0 μg/L, at Venado Tuerto City, Argentina), endosulfan (0.78 μg/L, at Yavtmal, Maharashtra, India), parathion (4.17 μg/L, at Akkar, Lebanon), endrin (3.48 μg/L, at KwaZuln-Natl Province, South Africa) and imidacloprid (1.53 μg/L, at Son-La province, Vietnam) are reported. Pesticides can be significantly removed through physical, chemical, and biological treatment. Mycoremediation technology has the potential for up to 90% pesticide removal from water resources. Complete removal of the pesticides through a single biological treatment approach such as mycoremediation, phytoremediation, bioremediation, and microbial fuel cells is still a challenging task, however, the integration of two or more biological treatment approaches can attain complete removal of pesticides from water resources. Physical methods along with oxidation methods can be employed for complete removal of pesticides from drinking water.

Type-wide biochars loaded with Mg/Al layered double hydroxide as adsorbent for phosphate and mixed heavy metal ions in water

This study discussed the adsorption of mixed heavy metal ions (Cu²⁺, Co²⁺, Pb²⁺) and phosphate ions by ten pristine biochars and those with precipitated Mg/Al layered double hydroxide (LDH). The pristine biochars have adsorption capacities of 6.9-13.4 mg/g for Cu²⁺, 1.1-9.7 mg/g for Co²⁺, 7.8-20.7 mg/g for Pb²⁺, and 0.8-4.9 mg/g for PO₄^3-. The LDH-biochars have markedly increased adsorption capacities of 20.4-25.8 mg/g for Cu²⁺, 8.6-15.0 mg/g for Co²⁺, 26.5-40.4 mg/g for Pb²⁺ with mixed metal ions, and 13.0-21.8 mg/g for PO₄^3-. Part of the Mg ions but Al ions are released from the LDH-biochars during adsorption, counting less than 7.2% of the adsorbed ions. The pristine biochars have specific adsorption sites for Cu²⁺ and Co²⁺, separate Pb²⁺ sites related to ether groups on biochar, and areal-dependent sites for PO₄^3-. There is no universal adsorption mechanism corresponding to mixed metal ion adsorption for individual pristine biochar involving different contributions of C-O-C, C-O-H, and CO groups and graphitic-N, pyrrolic-N, and pyridine-N groups. The LDH complexes with hydroxyl and carbonyl groups of biochar, and the LDH interacts with biochar's ether groups, which contributes to metal adsorption, against the conception that the biochar is merely a carrier of LDH as adsorbents.

Engineered biochar supported layered double hydroxide-cellulose nanocrystals composite-: Synthesis, characterization and azo dye removal performance

In this work, engineered biochar decorated layered double hydroxides and cellulose nanocrystals (B-CuFe-CNC) biocomposites were synthesized by the facile ultrasonicated-co-precipitation technique. The biocomposite was investigated for purification of Eriochrome Black T (EBT) dye from water. The characterization results showed that the presence of CNC in biochar-layered double hydroxides resulted in a two-dimensional rod-like structure with excellent crystallinity, improved surface functionalities, and provides an attractive platform for the enhanced adsorption of azo anionic dye molecules. The adsorption system was appropriately demonstrated by the BBD-RSM (R² > 0.994). The biocomposite exhibited higher EBT adsorption in the acidic pH range (2-5) due to strong electrostatic and chemical interactions. The kinetic and isotherm results were well demonstrated by pseudo-second order, Freundlich, and Redlich Peterson models. The maximum adsorption capacity of biocomposite was 876.2 mg/g achieved within 45 min. The spectroscopic analyses imply that the high removal of EBT by biocomposite is mainly governed by electrostatic attraction, hydrogen bonding, and chemical/metal complexation mechanisms. The biocomposite maintained high EBT removal after six successive adsorption cycles and excellent dye adsorption in the different water matrices. The results suggest that tailoring biochar properties with layered double hydroxide and CNC is a promising way for the enhanced removal of dye contaminants from wastewater.

Essence of hydroxyapatite in defluoridation of drinking water: A review

Hydroxyapatite (HAP) is an easily synthesizable, low-cost mineral that has been recognized as a potential material for fluoride removal. Some of the synthesis methods of HAP are quite straightforward and cost-effective, while some require sophisticated synthesis techniques under advanced laboratory conditions. This review assesses the physicochemical characteristics of HAP and HAP-based composites produced via various techniques, their recent development in defluoridation and most importantly, the fluoride removal performances. For the first time, fluoride removal performances of HAP and HAP composites are compared based on partition coefficient (K_D) instead of maximum adsorption capacity (Q_max), which is significantly influenced by initial loading concentrations. Novel HAP tailored composites exhibit comparatively high K_D values indicating the excellent capability of fluoride removal along with specific surface areas above 120 m²/g. HAP doped with aluminium complexes, HAP doped ceramic beads, HAP-pectin nanocomposite and HAP-stilbite nanocomposite, HAP decorated nanotubes, nanowires and nanosheets demonstrated high Q_max and K_D. The secret of HAP is not the excellent fluoride removal performances but best removal at neutral and near-neutral pH, which most of the defluoridation materials are incapable of, making them ideal adsorbents for drinking water treatment. Multiple mechanisms including physical surface adsorption, ion-exchange, and electrostatic interactions are the main mechanisms involved in defluoridation. Further research work must be focused on upscaling HAP-based composites for defluoridation on a commercial scale.

Simultaneous immobilization of arsenic, lead and cadmium by magnesium-aluminum modified biochar in mining soil

Owing to the human activities such as smelting and mining, arsenic (As), lead (Pb) and cadmium (Cd) seriously polluted the soil of non-ferrous metal mining areas, thus efficient methods for the simultaneous immobilization of the three heavy metals are urgently needed. In the present study, Mg-Al modified biochars (MABs) were synthesized through a simple one-pot pyrolysis method to immobilize the three heavy metals. According to the BET (Brunauer-Emmett-Teller) test method, MABs had larger specific surface areas than biochar. Compared to the materials obtained at 300 °C and 700 °C, MAB with a pyrolysis temperature of 500 °C (MAB 500) had a significant immobilization effect on As, Pb and Cd in the Gansu mining area. Compared with BC, the removal efficiencies of As, Pb and Cd increased from -62%, 17% and 5% to 52%, 100% and 66%, respectively. And the toxicity characteristic leaching procedure (TCLP) test showed that the leaching concentrations of the three heavy metals in the treated soil were all lower than the standard value. X-ray photoelectron spectroscopy and kinetic experiments showed that there were various mechanisms in the immobilization process of the three heavy metals, and the large specific surface area and the multi-Mg/Al-OH of MABs play an important role in this process. More charges were provided by larger specific surface for ion exchange with heavy metals. In addition, larger specific surface area also provided more adsorption sites. More complex sites were provided by Mg/Al-OH to form Mg/Al-O-M then immobilize the heavy metals. In summary, the immobilization mechanism may involve electrostatic attraction, precipitation/co-precipitation, and surface complexation.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.

Ethylenediaminetetraacetate functionalized MgFe layered double hydroxide/biochar composites for highly efficient adsorptive removal of lead ions from aqueous solutions

The application of layered double hydroxides (LDHs) of MgFe and its composites with biochar of Eucalyptus camdulensis (Eb) and ethylenediaminetetraacetic acid (EDTA) was explored in a batch study to mitigate toxic lead ions (Pb²⁺) from synthetic wastewater solutions. SEM images revealed that MgFe/LDH composites with Eb were successfully formed, while FTIR spectra confirmed the successful adsorption of Pb²⁺ onto the MgFe/LDH and composite adsorbents. Batch equilibrium was attained after 60 min, then the adsorption capacity gradually increased. An increase in adsorption capacity (and a 60% decrease in the percentage removal) was observed by increasing the initial Pb²⁺ concentration, and the highest value was 136 mg g^-1 for MgFe/LDH-Eb_EDTA. A 50–60% increase in both the adsorption capacities and percent removal was seen in the pH range of 2–6. The second-order kinetic model had a nearly perfect fitting, suggesting that chemisorption was the mechanism controlling adsorption. The Langmuir isotherm model best presented the adsorption data, suggesting that the Pb²⁺ adsorption was monolayer, and predicted a better affinity between the adsorbent surface and absorbed Pb²⁺ for MgFe/LDH-Eb_EDTA in comparison to the other two adsorbents. The D–R isotherm suggested that the adsorption system was physical based on E values for all three adsorbents, while the Temkin isotherm model suggested that Pb²⁺ adsorption was heterogeneous. Finally, the Sips and R–P isotherms predicted that the adsorption of Pb²⁺ on the surface of the adsorbents was homogeneous and heterogeneous.

Recovering metal ions from oxalic acid leaching palygorskite-rich clay wastewater to fabricate layered mixed metal oxide/carbon composites for high-efficient removing Congo red

This study developed a sustainable way to transform metallic residues in wastewater and spent adsorbents that adsorbed organic pollutants into novel high-efficiency adsorbents to treat water pollution again. The metal ions recovered from oxalic acid leaching palygorskite-rich clay wastewater was used to construct the hydrotalcite-like composites, after adsorbing organic pollutants, which was calcined and carbonized to convert into the mixed metal oxide/carbon composites (MMO/Cs). The fabricated MMO/Cs showed outstanding adsorption performance for the anionic azo dye Congo Red (CR). Especially, the MMO/C2 with the M²⁺/M³⁺ molar ratio of 2, which adjusted by supplementing Mg²⁺, had ultra-high adsorption capacity and ultra-clean removal efficiency for CR. The adsorption capacity was as high as 3303 mg/g, and only 0.5 g/L MMO/C2 dosing treatment for 6 h could completely decolor and remove the 2000 mg/L CR aqueous solution. Moreover, MMO/Cs exhibited the ability to simultaneous remove CR and Methylene blue (MB) mixed dye contaminants, and demonstrated the excellent recyclability. This work provides a promising method for the high-value conversion of waste resources and the synthesis of high-efficiency adsorbents.

Functionalized cotton charcoal/chitosan biomass-based hydrogel for capturing Pb2+, Cu2+ and MB

In this work, a porous multi-functional biomass carbon was prepared by acid-base modification method, which realized the reuse of waste cotton material. Then, the modified biochar was combined with the acrylic-based hydrogel by radical polymerization, and the biochar acrylic-based hydrogel (CS/EDTA/CBC) composite with chitosan and ethylenediamine tetraacetic acid was successfully prepared. This not only increases the adsorption performance of the adsorbent but also improves the stability of hydrogel. These characteristics provide high-efficiency adsorption capacity for pollutants (1105.78 mg g^-1 for Pb²⁺, 678.04 mg g^-1 for Cu²⁺, and 590.72 mg g^-1 for methylene blue (MB)), which is far superior to most reported adsorbents. Meanwhile, the adsorbent would have a strong chemical interaction with Pb²⁺ and Cu²⁺, can form a stable chelating structure, and showed stronger selective adsorption. The adsorption process is more suitable for the Langmuir isotherm and follows a pseudo-second-order kinetic model, which indicates that the adsorption is a single-layer adsorption, and the rate-limiting step is a chemical chelation reaction. XPS results confirmed that surface complexation and electrostatic attraction are the main mechanisms of the adsorption reaction. After five cycles, the adsorption capacity of the adsorbent and the recovery of heavy metal ions remained at a high level.

Layered double hydroxides loaded sludge biochar composite for adsorptive removal of benzotriazole and Pb(II) from aqueous solution

In this work, a novel sludge biochar/Zn-Al layered double hydroxide composite (SL) was synthesized in a facile co-precipitation method, and it was used to simultaneously remove benzotriazole (BTA) and lead ion (Pb(II)). Batch adsorption experiments demonstrated that composites with sludge content of 1.0 g (SL-1.0) had a great adsorption performance for BTA and Pb(II). The maximum adsorption capacities of SL-1.0 for BTA and Pb(II) were 239.6 and 226.1 mg g^-1, respectively. There was preferential adsorption of BTA in BTA and Pb(II) binary system. The adsorption mechanism analysis indicated that the BTA and Pb(II) adsorption involved electrostatic attraction and chemical bonding with surface functional groups on SL-1.0. Specifically, hydrogen bonding and π-π interaction were mainly ascribed to BTA adsorption, while complexation with surface function groups dominated Pb(II) adsorption. With the advantages of facile synthesis and excellent adsorption capacity, SL-1.0 possesses great potential for simultaneously removing of BTA and Pb(II) from wastewaters.

Size Selectivity of Anionic and Cationic Dyes Using LDH Modified Adsorbent with Low-Cost Rambutan Peel to Hydrochar

Modification of the layered double hydroxide of CuAl-LDHs by composite with hydrochar (HC) to form CuAl-HC LDH. Material characterization by XRD, FT-IR and SEM analysis was used to prove the success of the modification. The characterization of XRD and FT-IR spectra showed similarities to pure LDH and HC. Selectivity experiments were carried out by mixing malachite green, methylene blue, rhodamine-B, methyl orange, and methyl red to produce the most suitable methyl blue dye for CuAl-LDH, HC and CuAl-HC adsorbents. The effectiveness of CuAl-HC LDH as adsorbent on methylene blue adsorption was tested through several influences such as adsorption isotherm, thermodynamics, and adsorbent regeneration. CuAl-HC LDH adsorption isotherm data shows that the adsorption process tends to follow the Langmuir isotherm model with a maximum adsorption capacity of 175.439 mg/g with a threefold increase compared to pure LDH. The effectiveness of the adsorbent for repeated use reaches five cycles as evidenced by the maximum capacity regeneration data reaching 82.2%, 79.3%, 77.9%, 76.1%, and 75.8%. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

A Review on the Removal of Carbamazepine from Aqueous Solution by Using Activated Carbon and Biochar

Carbamazepine (CBZ), one of the most used pharmaceuticals worldwide and a Contaminant of Emerging Concern, represents a potential risk for the environment and human health. Wastewater treatment plants (WWTPs) are a significant source of CBZ to the environment, polluting the whole water cycle. In this review, the CBZ presence and fate in the urban water cycle are addressed, with a focus on adsorption as a possible solution for its removal. Specifically, the scientific literature on CBZ removal by activated carbon and its possible substitute Biochar, is comprehensively scanned and summed up, in view of increasing the circularity in water treatments. CBZ adsorption onto activated carbon and biochar is analyzed considering several aspects, such as physicochemical characteristics of the adsorbents, operational conditions of the adsorption processes and adsorption kinetics and isotherms models. WWTPs usually show almost no removal of CBZ (even negative), whereas removal is witnessed in drinking water treatment plants through advanced treatments (even >90%). Among these, adsorption is considered one of the preferable methods, being economical and easier to operate. Adsorption capacity of CBZ is influenced by the characteristics of the adsorbent precursors, pyrolysis temperature and modification or activation processes. Among operational conditions, pH shows low influence on the process, as CBZ has no charge in most pH ranges. Differently, increasing temperature and rotational speed favor the adsorption of CBZ. The presence of other micro-contaminants and organic matter decreases the CBZ adsorption due to competition effects. These results, however, concern mainly laboratory-scale studies, hence, full-scale investigations are recommended to take into account the complexity of the real conditions.

Application of layered double hydroxide-biochar composites in wastewater treatment: Recent trends, modification strategies, and outlook

In recent years, layered double hydroxide-biochar (LDH-BC) composites as adsorbents and catalysts for contaminants removal (inorganic anions, heavy metals, and organics) have received increasing attention and became a new research point. It is because of the good chemical stability, abundant surface functional groups, excellent anion exchange ability, and good electronic properties of LDH-BC composites. Hence, we offer an overall review on the developments and processes in the synthesis of LDH-BC composites as adsorbents and catalysts. Special attention is devoted to the strategies for enhancing the properties of LDH-BC composites, including (1) magnetic treatment, (2) acid treatment, (3) alkali treatment, (4) controlling metal ion ratios, (5) LDHs intercalation, and (6) calcination. In addition, further studies are called for LDH-BC composites and potential areas for future application of LDH-BC composites are also proposed.

Efficient recovery of phosphate from simulated urine by Mg/Fe bimetallic oxide modified biochar as a potential resource

The massive use of phosphate fertilizers in agriculture is costly and induces water pollution, calling for more sustainable phosphate sources in the context of the circular economy. Here we prepared a new adsorbent based on waste straw biochar modified with the Mg/Fe bimetallic oxide, namely the Mg/Fe biochar, to recover phosphate from the simulated urine as an possible phosphate fertilizer. About 90% phosphate was recovered from the simulated urine with a wide pH range of 3.0-9.0 and a maximum adsorption capacity of 206.2 mg/g, using 1 g/L of Mg/Fe modified biochar. A pseudo second-order kinetics and Sips model were proposed to fit the experimental data well, suggesting that the adsorption was controlled by physical and chemical processes, which is driven by electrostatic attraction, intra-particle diffusion, ion exchange and surface ligand exchange. Overall, the Mg/Fe biochar is renewable and can recover more than 70% of phosphate in the simulated urine after 5 cycles of reuse, which appears as a safe and efficient adsorbent to recycle phosphate from urine.

Layered double hydroxides and related hybrid materials for removal of pharmaceutical pollutants from water

Pharmaceuticals and their by-products are recalcitrant contaminants in water. Moreover, the high consumption of these drugs has many detrimental effects on body waters and ecosystems. In this timely review, the advances in molecular engineering of layered double hydroxides (LDH) that have been used for the removal of pharmaceutical pollutants are discussed. The approach starts from the strategies to obtain homogeneous synthesis of LDH that allow the doping and/or surface functionalization of different metals and oxides, producing heterojunction systems as well as composites with carbon and silica-based materials with high surface area. Adsorption is considered as a traditional removal of pharmaceutical pollutants, so the kinetic and mechanism of this phenomenon are analyzed based on pH, temperature, ionic strength, in order to obtain new insights for the formation of multifunctional LDH. Advanced oxidation methodologies, mainly heterogeneous photocatalysis and Fenton-like processes, stand out as the more efficient even to obtain the mineralization of the drugs. The LDH have the advantage of structural memory that favors regeneration processes. The reconstruction of calcined LDH can be used to improve drug removal, through a combination of adsorption capacity/catalytic activity. A meticulous analysis of the persistence, toxicity and bioaccumulation of the most common pharmaceuticals has allowed us to highlight the ability of the LDH to remove recalcitrant drugs at relatively low concentrations (ppm, ppb), in contrast to other mixed oxide nanostructures and homogeneous oxidation processes. In this sense, the mechanism of drug removal by LDH is discussed based on the importance of the use of composites, scavenger agents, Fenton and electro-Fenton processes, membranes, thin films and coatings, among others. In addition, the ecotoxicity of LDH is also reviewed to indicate that these layered structures can exhibit biocompatibility or high toxicity depending on the adsorbed drug and ions/metals that compose them. Undoubtedly, the LDH have a unique flexible structure with adsorption capacity and catalytic activity, facts that explain the important reasons for their extensive use in the environmental remediation of pharmaceutical pollutants from water.

Enhanced removal of Co(II) and Ni(II) from high-salinity aqueous solution using reductive self-assembly of three-dimensional magnetic fungal hyphal/graphene oxide nanofibers

Layer-structured graphene oxide excellent carrier for modifications; however, its poor recoverability and stability preclude its application in wastewater treatment fields. Herein, three-dimensional magnetic fungal hyphal/graphene oxide nanofibers (MFHGs) were assembled by a reductive self-assembly (RSA) strategy for the efficient capture of Co(II) and Ni(II) from high-salinity aqueous solution. The RSA strategy is inexpensive, eco-friendly and easy to scale up. The obtained MFHGs enhanced the dispersity and stability of graphene oxide and exhibited excellent magnetization and large coercivity, leading to satisfactory solid-liquid separation performance and denser sediment. The results of batch removal experiments showed that the maximum removal capacity of MFHGs for Ni(II) and Co(II) was 97.44 and 104.34 mg/g, respectively, in 2 g/L Na₂SO₄ aqueous solution with a pH of 6.0 at 323 K, and the effects of initial pH and ionic strength on Co(II) and Ni(II) removal were explored. Yield residue analysis indicated that the high porosity and oxygen-containing functional groups of MFHGs remarkably improved their Co(II)- and Ni(II)-removal capacities. According to the analysis, hydroxyl groups and amine groups participated in the chemical reaction of Co(II) and Ni(II) removal, and cation-exchange chemical adsorption was dominant during the Co(II)- and Ni(II)-removal process. Based on the attributes of MFHGs, a continuous-flow recycle reactor (CFRR) was proposed for emergency aqueous solution treatment and exhibited satisfactory removal efficiency and regeneration performance. The combination of MFHGs and the proposed CFRR is a promising water treatment strategy for rapid treatment applications.

Application of macroalgal biomass derived biochar and bioelectrochemical system with Shewanella for the adsorptive removal and biodegradation of toxic azo dye

The present study aimed towards adsorptive removal of the toxic azo dye onto biochar derived from Eucheuma spinosum biomass. Characterization of the produced biochar was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). Eucheuma spinosum biochar (ES-BC) produced at 600 °C revealed a maximum adsorption capacity of 331.97 mg/g towards reactive red 120 dye. The adsorption data fitted best to the pseudo-second order kinetics (R² > 0.99) and Langmuir isotherm (R² > 0.98) models. These adsorption models signified the chemisorption mechanism with monolayer coverage of the adsorbent surface with dye molecules. Furthermore, the adsorption process was mainly governed by electrostatic interaction, ion exchange, metal complexation, and hydrogen bonding as supported by the solution pH, FTIR, XPS, and XRD investigation. Nevertheless, alone adsorption technology could not offer a complete solution for eliminating the noxious dyes. Therefore, the bioelectrochemical system (BES) equipped with previously isolated marine Shewanella marisflavi BBL25 was intended for the complete remediation of azo dye. The BES II demonstrated highest dye decolorization (97.06%) within 48 h at biocathode where the reductive cleavage of the azo bond occurred. Cyclic voltammetry (CV) studies of the BES revealed perfect redox reactions taking place where the redox mediators shuttled the electrons to the dye molecule to accelerate the dye decolorization. Besides, the GC-MS analysis revealed biotransformation of the dye into less toxic metabolites as tested using a phyto and cytogenotoxicity.

Selective removal of anionic and cationic dyes by magnetic Fe3O4-loaded amine-modified hydrochar

Fe₃O₄-loaded protonated amine-modified hydrochar (Fe₃O₄-PAMH) was successfully prepared and characterized by scan electron microscopy equipped with energy-dispersion X-ray spectroscopy, zeta potential analysis, vibration sample magnetometry, Fourier transform infrared and X-ray photoelectron spectroscopies, Brunauer-Emmett-Teller measurement, and X-ray diffraction. Adsorption properties of Fe₃O₄-PAMH to negatively-charged methyl orange (MO) or positively-charged methylene blue (MB) in one- or two-component systems were evaluated. The Fe₃O₄-PAMH selectively adsorbed MO and MB at pH 5 and 11, respectively. The maximum MO and MB uptake capacities of Fe₃O₄-AMHC were 202.02 mg/g (pH 5.0) and 148.84 mg/g (pH 11) respectively. The Fe₃O₄-PAMH can be reused with simple pH management in adsorption-desorption cycles. The MB and MO adsorption abilities on Fe₃O₄-PAMH were maintained above 99% and 75% for five consecutive recycles, respectively. Thus, Fe₃O₄-PAMH shows powerful potential in efficiently and selectively adsorbing anionic or cationic dyes from mixed wastewater.

Advanced drug delivery applications of layered double hydroxide

Layered double hydroxides (LDHs), also known as anionic clays or hydrotalcite-like compounds, are a class of nanomaterials that attained great attention as a carrier for drug delivery applications. The lamellar structure of this compound exhibits a high surface-to-volume ratio which enables the intercalation of therapeutic agents and releases them at the target site, thereby reducing the adverse effect. Moreover, the intercalated drug can be released in a sustained manner, and hence the frequency of drug administration can be decreased. The co-precipitation, ion exchange, manual grinding, and sol-gel methods are the most employed for their synthesis. The unique properties like the ease of synthesis, low cost, high biocompatibility, and low toxicity render them suitable for biomedical applications. This review presents the advances in the structure, properties, method of preparation, types, functionalization, and drug delivery applications of LDH. Also, this review provides various new conceptual insights that can form the basis for new research questions related to the drug delivery applications of LDH.