Synthesis of an attapulgite clay@carbon nanocomposite adsorbent by a hydrothermal carbonization process and their application in the removal of toxic metal ions from water

Metal-Organic Framework-Based Materials for Wastewater Treatment: Superior Adsorbent Materials for the Removal of Hazardous Pollutants

In previous years, different pollutants, for example, organic dyes, antibiotics, heavy metals, pharmaceuticals, and agricultural pollutants, have been of note to the water enterprise due to their insufficient reduction during standard water and wastewater processing methods. MOFs have been found to have potential toward wastewater management. This Review focused on the synthesis process (such as traditional, electrochemical, microwave, sonochemical, mechanochemical, and continuous-flow spray-drying method) of MOF materials. Moreover, the properties of the MOF materials have been discussed in detail. Further, MOF materials' applications for wastewater treatment (such as the removal of antibiotics, organic dyes, heavy metal ions, and agricultural waste) have been discussed. Additionally, we have compared the performances of some typical MOFs-based materials with those of other commonly used materials. Finally, the study's current challenges, future prospects, and outlook have been highlighted.

Low-temperature aerobic carbonization and activation of cellulosic materials for Pb2+ removal in water source

Targeting the removal of Pb²⁺ in wastewater, cellulosic materials were carbonized in an aerobic environment and activated via ion exchange. The maximum adsorption capacity reached 243.5 mg/g on an MCC-derived adsorbent activated with sodium acetate. The modified porous properties improved the adsorption capacity. The capacity could be completely recovered five times through elution with EDTA. Because of the negative effects of Ni, Mg, and Ca elements, the adsorption capacities of activated carbonized natural materials were lower than that of pure cellulose. N₂ adsorption measurement showed that the adsorbent had a large specific surface area as well as abundant micropores and 4-nm-sized mesopores. FTIR and surface potential results proved that carboxyl group was generated in the aerobic carbonization, and was deprotonated during ion exchange. This adsorbent consisted of C-C bonds as the building blocks and hydrophilic groups on the surface. XPS results demonstrated that the Pb 4f binding energies were reduced by 0.7-0.8 eV due to the interaction between Pb²⁺ and the activated adsorbent, indicating that the carboxylate groups bonded with Pb²⁺ through coordination interactions. Pseudo-second-order and Elovich kinetic models were well fitted with the adsorption processes on the pristine and activated carbonized adsorbents, indicative of chemisorption on heterogeneous surfaces. The Freundlich expression agreed well with the data measured, and the pristine and activated adsorbents had weak and strong affinities for Pb²⁺, respectively. The Pb²⁺ adsorption process was exothermic and spontaneous, and heat release determined the spontaneity. The adsorption capacity is attributed to the carboxylate groups and pores generated in the aerobic oxidation and ion exchange procedures.

Recent trends and challenges with the synthesis of membranes: Industrial opportunities towards environmental remediation

The industrial and agricultural revolution has posed a serious and potential threat to environment. The industrial and agricultural pollutants are directly released into the environment. This issue has clinched the scientists to work on different materials in order to decontaminate the environment. Among all other techniques, the membrane filtration technology has fascinated researchers to overcome the pollution by its promising features. This review elaborated various membrane synthesis approaches along with their mechanism of filtration, their applications towards environmental remediation such as removal of heavy metals, degradation of dyes, pharma waste, organic pollutants, as well as gas sensing applications. The membrane synthesis using different sort of materials in which inorganic, carbon materials, polymers and metal organic framework (MOFs) are highlighted. These materials have been involved in synthesis of membrane to make it more cost effective and productive to remove such hazardous materials from wastewater. Based on the reported literature, it has been found that inorganic and polymer membranes are facing issues of brittleness and swelling prior to the industrial scale applications related to the high temperature and pressure which needs to be addressed to enhance the permeation performance.

Purinoceptor Targeted Cytotoxicity of Adenosine Triphosphate-Conjugated Biogenic Selenium Nanoparticles in Human Colon Cancer Cells

The adenosine triphosphate (ATP)-conjugated biogenic selenium nanoparticles (SeNPs) for P2 (purinoceptors) receptor-targeted anti-colon cancer activity were developed in this study. First, the SeNPs were synthesized using Trichoderma extracts (TE) and then conjugated with ATP to enhance their anticancer activity. The developed SeNPs had an oval crystalline structure with an average diameter size of 26.45 ± 1.71 d. nm, while the ATP-SeNPs were 78.6 ± 2.91 d. nm. The SeNPs contain Se, and less persistence of P while the ATP-SeNPs have high level of P, and Se in the energy-dispersive spectroscopy (EDS). Further, both nanoparticles exhibited larger sizes in the dynamic light scattering (DLS) analysis than in the transmission electron microscopy (TEM) analysis. The DLS and Fourier transform infrared spectroscopy (FTIR) results provide evidence that the amine group (-NH2) of ATP might bind with the negatively charged SeNPs through covalent bonding. The IC50 concentration was 17.25 ± 1.16 µg/mL for ATP-SeNPs and 61.24 ± 2.08 µg/mL against the caco-2 cell line. The IC50 results evidenced the higher cytotoxicity of ATP-SeNPs in the caco-2 cell line than in HEK293 cells. ATP-SeNPs trigger the anticancer activity in the caco-2 cell line through the induction of mitochondrial membrane potential (MMP) loss and nucleus damage. The biocompatibility test of hemolysis and the egg CAM assay confirmed the non-toxicity of these nanoparticles. Overall, the results proved that the newly developed ATP-SeNPs exhibited higher cytotoxicity in the caco-2 cell line than SeNPs. However, further molecular and in vivo experiments are required to develop the ATP-SeNPs as a candidate drug for cancer-targeted therapeutics.

Synthesis, Characterization, and Application of Co-Al-Zn Layered Double Hydroxide/Hydrochar Composite for Simultaneous Removal of Cationic and Anionic Dyes

Decontamination of organic dyes from wastewater requires efficient and compatible materials that must be able to remove dyes with different charges at the same time. In this study, composites of layered double hydroxide (LDH) and hydrochar (HC) were prepared and tested for use as general-purpose sorbents for the simultaneous removal of cationic and anionic dyes (i.e., methylene blue (MB), methyl orange (MO), and reactive yellow (RY)). Characterization studies reveal that the surface functional groups on composites are –OH, NO3, M–O bonds. It was observed that crystallinity of LDH decreased with an increasing amount of HC. Preliminary experiments showed that the dyes (i.e., MB, MO, and RY) were well removed simultaneously onto the composite with HC (2.0 g HC/prepared composite). This composite was selected for more experiments, and the adsorption efficiency was optimized by the multivariate technique using the response surface methodology (RSM). Removal efficiency of 100% was obtained for all three dyes with an adsorption capacity of 243, 5.3, and 16.3 µmol g−1 for MB, MO, and RY, respectively. Elovich’s initial intake rates (α) were 4,272, 441, and 99.5 mg g−1 min−1 for RY, MB, and MO, respectively. Data fitted in various models suggested second-order multiplex kinetics, where the surface heterogeneity response was sorbate dependent.

Prediction of lead (Pb) adsorption on attapulgite clay using the feasibility of data intelligence models

This study investigates the performance of support vector machine (SVM), multivariate adaptive regression spline (MARS), and random forest (RF) models for predicting the lead (Pb) adsorption by attapulgite clay. Models are constructed using batch stochastic data of heavy metal (HM) concentrations under different physicochemical conditions. Implementation of auto-hyper-parameter tuning using grid-search approach and comparative analysis is performed against the benchmark artificial intelligence (AI) models. Models are constructed based on Pb concentration (IC), the dosage of attapulgite clay (dose), contact time (CT), pH, and NaNO3 (SN). Principle component analysis (PCA) and correlation analysis (CA) methods are integrated to assess the importance of the applied predictors and their relationship with the target. Research findings approved the potential of the grid-RF model as a marginal superior predictive model against the grid-SVM in terms of MAE, i.e., 3.29 and 3.34, respectively; moreover, the md scored the same, i.e., 0.93, which reveals the potential predictability for both. Nonetheless, grid-MARS and standalone MARS models remained likewise in their predictability. IC parameter demonstrated the highest influential among all the predictors with the highest value of importance in the case of all three evaluators. The solution pH and dose stands together with marginal differences in case of PCA method; however, solution pH and CT appeared with similarity impact using the PCA method.

Preparation and application of carbon and hollow TiO2 microspheres by microwave heating at a low temperature

A fast, simple, and energy-saving microwave-assisted approach was successfully developed to prepare carbon microspheres. The carbon microspheres with a uniform particle size and good dispersity were prepared using glucose as the raw material and HCl as the dehydrating agent at low temperature (90°C) in an open system with the assistance of microwave heating. The carbon microspheres were characterized by elemental analysis, XRD, SEM, FTIR, TG, and Raman. The results showed that the carbon microspheres prepared under the condition of 18.5% (v/v) HCl and heating for 30 min by microwave had a narrow size distribution. The core–shell structure of the carbon core and TiO2 shell was prepared with (NH4)2TiF6, H3BO3 using the microwave-assisted method. The hollow TiO2 microspheres with good crystallinity and high photocatalytic properties were successfully prepared by sacrificing the carbon microspheres.

Novel composites with a cross-linked polyaniline shell and oriented palygorskite as ideal microwave absorbers

The obtained composites exhibit a cross-linked shell structure, which has a positive effect on the microwave absorption performance of the materials.

Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation

Targeting the removal of Pb²⁺ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca²⁺, a common cation in natural water, the Pb²⁺ adsorption capacity slightly declined. In contrast, Mg²⁺ obviously prohibited the adsorption for Pb²⁺. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb²⁺ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f_5/2 and Pd 4f_7/2 XPS spectra of Pb²⁺ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO₃)₂, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb²⁺ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.

Surface Properties of Halloysite-Carbon Nanocomposites and Their Application for Adsorption of Paracetamol

Analysis of surface properties of halloysite-carbon nanocomposites and non-modified halloysite was carried out with surface sensitive X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography (IGC). The XPS spectra were measured in a wide range of the electron binding energy (survey spectra) and in the region of C 1s photoelectron peak (narrow scans). The IGC results show the changes of halloysite surface from basic for pure halloysite to acidic for carbon-halloysite nanocomposites. Halloysite-carbon nanocomposites were used as adsorbents of paracetamol from an aqueous solution. The adsorption mechanism was found to follow the pseudo-second-order and intra-particle diffusion models. The Langmuir multi-center adsorption model described well the obtained experimental data. The presence of carbon increased significantly the adsorption ability of halloysite-carbon nanocomposites for paracetamol in comparison to the non-modified halloysite.

Insight into β-cyclodextrin polymer microsphere as a potential filtration reducer in water-based drilling fluids for high temperature application

Controlling the filtration of water-based drilling fluid effectively in high temperature environment is a great challenge in drilling engineering. In this study, β-cyclodextrin polymer microspheres (β-CDPMs) were synthesized by crosslinking between β-cyclodextrin and epichlorohydrin via inverse emulsion polymerization and employed as filtration reducers. The standard American Petroleum Institute filtration test showed that the β-CDPMs can only perform the enhanced filtration control ability at temperatures above 160 °C, and can tolerate the temperature resistance up to 240 °C without significant influence of rheology. As the thermal aging temperature is above 160 °C, numerous nano carbon spheres and nanostructured composites generated due to the occurrence of hydrothermal reaction. These high temperature stable nanoparticles bridged across the nano sized gaps and participated into forming dense filter cake, contributing to excellent filtration control. The filtration control mechanism proposed in this study opened a novel avenue for high temperature filtration control in water-based drilling fluids.

Gelation, Liquid Crystalline Behavior, and Ionic Conductivity of Nanocomposite Ionogel Electrolytes Based On Attapulgite Nanorods

Anisotropic nanoparticles and their dispersions have attracted much attention because of their distinguished characteristics and promising applications. In this study, the novel liquid crystalline nanocomposite ionogel electrolyte materials based on anisotropic nanoparticles of attapulgite (ATP) have been prepared. The gelation, liquid crystalline (LC) behavior, thermal stability, and ionic conductivity were systematically investigated. Rheological, polarized optical microscopy (POM), and small-angle X-ray scattering (SAXS) measurements demonstrated that these liquid crystalline ionogels showed a two-step mechanism consisting of gelation and subsequent reorganization of the gel. Interestingly, the obtained ionogel electrolytes were very stable and LC gel structures were not destroyed even though the temperature was as high as 200 °C. Furthermore, these ionogels possessed outstanding thermal stability and the decomposition temperature exceeded 400 °C. Remarkably, the LC nanocomposite ionogel electrolytes exhibited high room temperature ionic conductivity and the value still exceeded 1.0 × 10^-3 S/cm even when the ATP concentration up to 30 wt %. These novel findings are very useful for the fabrication of high temperature resistant electrochemical devices and liquid crystalline nanocomposite materials.

Magnetic Mg-Fe/LDH Intercalated Activated Carbon Composites for Nitrate and Phosphate Removal from Wastewater: Insight into Behavior and Mechanisms

This experimental work focused on the synthesis, characterization, and testing of a unique, magnetically separable, and eco-friendly adsorbent composite material for the advanced treatment and efficient removal of nitrate and phosphate pollutants from wastewater. The MgAl-augmented double-layered hydroxide (Mg-Fe/LDH) intercalated with sludge-based activated carbon (SBAC-MgFe) composites were characterized by FT-IR, XRD, BET, VSM, SEM, and TEM techniques, revealing homogeneous and efficient dispersion of MgFe/LDH within the activated carbon (AC) matrix, a highly mesoporous structure, and superparamagnetic characteristics. The initial solution pH, adsorbent dose, contact time, and temperature parameters were optimized in order to reach the best removal performance for both pollutants. The maximum adsorption capacities of phosphate and nitrate were found to be 110 and 54.5 mg/g, respectively. The competition between phosphate and coexisting ions (Cl⁻, CO₃²⁻, and SO₄²⁻) was studied and found to be remarkably lower in comparison with the nitrate adsorption. The adsorption mechanisms were elucidated by kinetic, isotherm, thermodynamic modeling, and post-adsorption characterizations of the composite. Modeling and mechanistic studies demonstrated that physisorption processes such as electrostatic attraction and ion exchange mainly governed the nitrate and phosphate adsorption. The composite indicated an outstanding regeneration performance even after five sequences of adsorption/desorption cycles. The fabricated composite with magnetically separable characteristics can be used as a promising adsorbent for the removal of phosphate and nitrate pollutants from wastewater.

Graphene oxide/polydimethylsiloxane composite sponge for removing Pb(ii) from water

An efficient adsorbent to remove Pb(ii) from water was prepared by treating polydimethylsiloxane (PDMS) sponge with polyvinyl alcohol and then coating the sponge with graphene oxide (GO). The GO-PDMS sponge was highly hydrophilic, easily handled during and after use, and easily recycled. The kinetics and isotherms of Pb(ii) sorption onto the GO-PDMS sponge were investigated by performing batch sorption tests. The kinetics of Pb(ii) sorption onto the GO-PDMS sponge indicated that sorption equilibrium occurred rapidly (within 60 min) and that the sorption data could be described using a pseudo-second-order model. Maximum Pb(ii) sorption onto the GO-PDMS sponge occurred at pH > 5. Increasing GO loading on the PDMS sponge increased the amount of Pb(ii) that could be sorbed. The isotherm for Pb(ii) sorption onto the GO-PDMS sponge was non-linear and was well described by the Langmuir isotherm model, indicating that Pb(ii) sorption onto the GO-PDMS sponge was homogeneous and occurred through sorption of a monolayer of Pb(ii). The GO-PDMS sponge, used as a filter, removed Pb(ii) efficiently from water. The Pb(ii) removal efficiencies were more than 50% and the maximum was 85%.

Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption

Understanding surface and interfacial information, which has a close relationship to the structures and properties of materials, helps guide the design of materials for specific applications. This study focuses on the surface functionalization of montmorillonite (Mt) with chitosan (CTS) and exploring the role of surface properties on its adsorptive performance. Two prototypical products, namely, 180-Htc@Mt and 250-Htc@Mt, were fabricated via the hydrothermal method at 180 and 250 °C, respectively. Field emission scanning electron microscopy revealed that hydrothermal carbon (Htc) derived from CTS anchored on the surface of Mt uniformly with a spherical morphology. The introduction of Htc endowed the surface of Mt with abundant hydroxy, amine, and amide groups; organic carbon; developed porosity; and hydrophobic interfacial property. Hydrothermal temperature has huge impacts on the surface system, and smaller particles (average size of 27 vs 53 nm) with deeper carbonization, higher content of carbonaceous and nitrogenous functional groups, more developed porosity (66.149 vs 39.434 m²/g of specific surface area, 0.115 vs 0.090 cm³/g of pore volume), and slightly decreased hydrophobicity can be readily achieved at a higher temperature. The incoming surface protonated amine and amide functional groups show an ion-dipolar interaction to polar aflatoxin B₁ (AFB₁), and the increased organic carbon content as well as interfacial hydrophobicity generate a hydrophobic interaction to weak polar zearalenone (ZER). Consequently, the surface functionalization affords Mt enhanced adsorption capacity for AFB₁, approximately two times compared with Mt, and superior adsorption ability for ZER (10 mg/g). The present work provides sufficient evidence of "surface directs application" of Mt, which encourages researchers to focus on studies of the surface science of clay minerals.

Chromium(III) Removal from Wastewater by Chitosan Flakes

Chitosan is very effective in removing metal ions through their adsorption. A preliminary investigation of the adsorption of chromium(III) by chitosan was carried out by means of batch tests as a function of contact time, pH, ion competition, and initial chromium(III) concentration. The rate of adsorption was rather rapid (t1/2 < 18 min) and influenced by the presence of other metal ions. The obtained data were tested using the Langmuir and Freundlich isotherm models and, based on R2 values, the former appeared better applicable than the latter. Chitosan was found to have an excellent loading capacity for chromium(III), namely 138.0 mg Cr per g of chitosan at pH = 3.8, but metal ions adsorption was strongly influenced by the pH. About 76% of the recovered chromium was then removed simply by washing the used chitosan with 0.1 M EDTA (Ethylenediaminetetraacetic acid) solution. This study demonstrates that chitosan has the potential to become an effective and low-cost agent for wastewater treatment (e.g., tannery waste) and in situ environmental remediation.

Electrical-Driven Release and Migration of Herbicide Using a Gel-Based Nanocomposite

In this work, an electrical-driven release and migration glyphosate (EDRMG) was fabricated using a nanocomposite made up of attapulgite (ATP), glyphosate (Gly), and calcium alginate (CA). Therein, ATP-CA acted as a nanonetwork-structured carrier to efficiently load plenty of Gly to form porous ATP-Gly-CA hydrogel spheres (actually EDRMG-0.5) via a cross-linking reaction. The pores in EDRMG-0.5 hydrogel spheres were enlarged under an electric field because of the Coulomb force of the anionic CA polymer, and the release of negatively charged Gly from the spheres could be driven by the electric field force. Thus, EDRMG-0.5 exhibited a great electroresponsively controlled-release property, which was confirmed by a pot experiment. Importantly, the EDRMG-0.5 hydrogel spheres had fine biocompatibility on fish and mice, displaying good biosafety. This work provides a low cost and promising approach to control Gly release, deliver Gly precisely, and improve utilization efficiency, which might have a high application value.

Sorption process of municipal solid waste biochar-montmorillonite composite for ciprofloxacin removal in aqueous media

This study evaluates a novel adsorbent for ciprofloxacin (CPX) removal from water using a composite derived from municipal solid waste biochar (MSW-BC) and montmorillonite (MMT). The composite adsorbent and pristine materials were characterized using powder X-Ray Diffraction (PXRD), Fourier-Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscope (SEM) before and after the adsorption. Batch experiments were conducted to study the mechanisms involved in the adsorption process. Ciprofloxacin sorption mechanisms were interpreted in terms of its pH-dependency and the distribution coefficients. The SEM images confirmed the successful binding of MMT onto the MSW-BC through flaky structure along with a porous morphology. Encapsulation of MMT onto MSW-BC was exhibited through changes in the basal spacing of MMT via PXRD analysis. Results from FTIR spectra indicated the presence of functional groups for both pristine materials and the composite that were involved in the adsorption reaction. The Hill isotherm model and pseudo-second-order and Elovich kinetic models fitted the batch sorption data, which explained the surface heterogeneity of the composite and cooperative adsorption mechanisms. Changes made to the MSW-BC through the introduction of MMT, enhanced the active sites on the composite adsorbent, thereby improving its interaction with ionizable CPX molecules giving high sorption efficiency.

Synthesis and Characterization of Halloysite/Carbon Nanocomposites for Enhanced NSAIDs Adsorption from Water

The adsorption of ketoprofen, naproxen, and diclofenac (non-steroidal anti-inflammatory drugs, NSAIDs) on halloysite/carbon nanocomposites and non-modified halloysite were investigated in this work. Halloysite/carbon nanocomposites were obtained through liquid phase impregnation and carbonization using halloysite as the template and saccharose as the carbon precursor. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FT-IR), and low-temperature nitrogen adsorption method were employed to study the morphological and structural changes of the halloysite/carbon nanocomposites. The effects of contact time, initial concentration of adsorbates, pH of solution, and mass of adsorbent on the adsorption were studied. Adsorption mechanism was found to fit pseudo-second-order and intra-particle diffusion models. The obtained experimental adsorption data were well represented by the Langmuir multi-center adsorption model. Adsorption ability of halloysite/carbon nanocomposites was much higher for all the studied NSAIDs in comparison to non-modified halloysite. Optimized chemical structures of ketoprofen, naproxen, and diclofenac obtained by Density Functional Theory (DFT) calculation showed that charge distributions of these adsorbate molecules and their ions can be helpful to explain the details of adsorption mechanism of NSAIDs on halloysite/carbon nanocomposites.

Functionalized Biochar/Clay Composites for Reducing the Bioavailable Fraction of Arsenic and Cadmium in River Sediment

Biochar has frequently been used for the treatment of heavy metal pollution in water and soil; its effect on contaminated sediments requires further research. To improve the ability of biochar to immobilize heavy metals in sediment, we prepared a functionalized biochar/attapulgite composite by pyrolysis of the clay attapulgite and zinc chloride-pretreated rice straw biomass. Compared with the original biochar, the biochar/attapulgite composite had a large increase in specific surface area, pore volume, oxygen-containing functional groups, and cation exchange capacity. Biochar effectively improved the dispersibility of attapulgite as a matrix. The results showed that the biochar/attapulgite composite effectively reduced the bioavailable fraction of arsenic (As) and cadmium (Cd) in river sediment, which was a great improvement compared with the raw biochar. After the sediment was treated with different biochar/attapulgite composites, the concentrations of As and Cd in the overlying water and the porewater, and the content of acid-extractable and toxicity characteristic leaching procedure (TCLP)-extractable As and Cd in the solid phase of the sediment decreased significantly. Both zinc chloride activation and attapulgite improved As and Cd immobilization in sediment when we used the biochar/attapulgite composite. The results suggest that biochar/attapulgite composite can be used as an efficient in situ sorbent amendment to improve the heavy metal immobilization ability of the sediment. Environ Toxicol Chem 2019;38:2337-2347. © 2019 SETAC.

Facile synthesis of graphene oxide/palygorskite composites for Pb(II) rapid removal from aqueous solutions

As a kind of earth-abundant and cheap natural clay mineral, palygorskite (Pal) was facilely modified by grafting with graphene oxide (GO) to fabricate GO/Pal composites for rapid removal of Pb(II) from aqueous solutions. The results of characterization confirmed that the GO/Pal composites were successfully grafted between GO sheets and Pal nanorods. The effects of pH, adsorbent dosage, adsorption time, initial Pb(II) concentration and temperature on the adsorption of Pb(II) onto the GO/Pal composites as adsorbents were systematically investigated. The maximum adsorption capacity over 106.6 mg/g was obtained within a short adsorption time of less than 1 h even at 298.15 K. The adsorption of Pb(II) was a fast process that more accurately followed the pseudo-second-order kinetic equation. This process also could be described better with the Langmuir equation model than the Freundlich model. The negative values of ΔG° and the positive values of ΔH° and ΔS° indicated that it was a spontaneous, endothermic and entropy-increasing adsorption process. Compared with pristine Pal and GO powders, such the GO/Pal composites as a cost-efficient and eco-friendly adsorbents could significantly improve the adsorption properties of Pb(II) and would have potential application in the industrial wastewater treatment for rapid removal of Pb(II).

Sustainable and scalable in-situ synthesis of hydrochar-wrapped Ti3AlC2-derived nanofibers as adsorbents to remove heavy metals

To ensure a sustainable future, it is imperative to efficiently utilize abundant biomass to produce such as platform chemicals, transport fuels, and other raw materials; hydrochar is one of the promising candidates derived by hydrothermal carbonization of biomass in pressurized hot water. The synthesis of "hydrochar-wrapped Ti₃AlC₂-derived nanofibers" was successfully achieved by a facile one-pot hydrothermal reaction using glucose as the hydrochar precursor. Meanwhile, cellulose and pinewood sawdust as raw materials were also investigated. Products were characterized by XRD, N₂ adsorption-desorption isotherms, SEM, TEM and FT-IR to investigate their crystal structures, textural properties, morphologies, and surface species. In the adsorption test to remove Cd(II) and Cu(II) in aqueous solution, hydrochar-wrapped nanofibers outperformed pure nanofibers derived from Ti₃AlC₂, hydrothermal carbon derived from glucose and commercial activated carbon. Finally, the regeneration, sorption kinetics, and possible adsorption mechanism were also explored.

Carbon-coated montmorillonite nanocomposite for the removal of chromium(VI) from aqueous solutions

A carbon-coated montmorillonite nanocomposite (CMt), obtained by hydrothermal carbonization of montmorillonite suspension in glucose, was used to remove Cr(VI) from aqueous solutions. The distribution and speciation of Cr immobilized by CMt were assessed by transmission electron microscopy with energy-dispersive X-ray analysis, X-ray absorption near edge structure (XANES), and scanning transmission soft X-ray microscopy (STXM). The variation in the functional groups and molecular structures of CMt was also investigated. The capacity of CMt for adsorbing Cr(VI) was markedly superior to that of the parent montmorillonite, showing maximum uptake of 100 and 12.4 mg g^-1 at pH 2 and 8, respectively. The Cr K-edge XANES and STXM analyses indicated that Cr(VI) was reduced to Cr(III) under both acidic and alkaline conditions, while a Cr(OH)₃ precipitate and Cr(III)-acetate complex were the predominant species present on the CMt surface. The Fourier transform infrared spectroscopy and C K-edge XANES further suggested that the phenolic groups in CMt could serve as electron donors, facilitating Cr(VI) reduction. The combined results indicate that electrostatic attraction, Cr(VI) reduction, complexation, and precipitation are involved in the removal of Cr(VI) by CMt.

β-cyclodextrin functionalized biochars as novel sorbents for high-performance of Pb2+ removal

The aim of this study was to synthesize the functionalized biochars with β-cyclodextrin (β-CD), compare the two kinds of adsorption capability, and try to explore the possible mechanism for the adsorption Pb²⁺ by β-CD functionalized rice straw and palm biochars in the aquatic environment. The performance of the functionalized biochars was matched against the activated and raw biochars. Rice straw biochar loaded with β-CD performed better than functionalized palm biochar with the adsorption capabilities of 130.60 mg/g and 90.30 mg/g at Pb²⁺ concentration of 3000 mg/L and 2000 mg/L, respectively. Maximum adsorption capability of functionalized rice straw and palm biochars from the Langmuir isotherms were all fitted out to be 131.24 mg/g and 118.08 mg/g for Pb²⁺. Kinetics and thermodynamics are combined to investigate the Pb²⁺ removal by the two functionalized biochars, e.g, Pb²⁺ is mainly removed by chemical process for functionalized palm biochar, whereas by both physical and chemical factors for functionalized rice straw biochar.

New micro/mesoporous nanocomposite material from low-cost sources for the efficient removal of aromatic and pathogenic pollutants from water

A new micro/mesoporous hybrid clay nanocomposite prepared from kaolinite clay, Carica papaya seeds, and ZnCl2 via calcination in an inert atmosphere is presented. Regardless of the synthesis temperature, the specific surface area of the nanocomposite material is between ≈150 and 300 m2/g. The material contains both micro- and mesopores in roughly equal amounts. X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy suggest the formation of several new bonds in the materials upon reaction of the precursors, thus confirming the formation of a new hybrid material. Thermogravimetric analysis/differential thermal analysis and elemental analysis confirm the presence of carbonaceous matter. The new composite is stable up to 900 °C and is an efficient adsorbent for the removal of a water micropollutant, 4-nitrophenol, and a pathogen, E. coli, from an aqueous medium, suggesting applications in water remediation are feasible.

Construction of spindle structured CeO2 modified with rod-like attapulgite as a high-performance photocatalyst for CO2 reduction

In this study, a spindle structured CeO₂ photocatalyst modified with rod-like attapulgite (CeO₂/ATP) was successfully prepared by simple high temperature calcination.

Porous biochar composite assembled with ternary needle-like iron-manganese-sulphur hybrids for high-efficiency lead removal

Hierarchical porous biochar derived from corn straw containing ternary needle-like iron-manganese-sulphur composites (Fe-Mn-S@HCS) are fabricated, and their physicochemical characteristics and performance for Pb removal were examined in detail. Introduction of Mn (transition metal) into Fe-biochar composites can effectively alter the chemical state of Fe; simultaneous doping with S can enhance cation exchange for Pb removal. High uptake of Pb by Fe-Mn-S@HCS in a short time period was observed with the adsorption capacity of 181.5 mg g^-1 and the pseudo-second-order rate constant of 0.075 g mg^-1 h^-1. Complexation, reduction, and precipitation were found to be involved in the Pb removal by Fe-Mn-S@HCS based on the results of HRTEM, XPS, and XRD analyses. This study demonstrated the feasibility of Fe-Mn-S biochar composites for high-efficiency Pb removal from aqueous solution.

Performance of ceria/iron oxide nano-composites based on chitosan as an effective adsorbent for removal of Cr(VI) and Co(II) ions from aqueous systems

A novel chitosan/ceria/iron oxide (CS/ceria/Fe₃O₄) nano-composite adsorbent was synthesized for removal of Cr(VI) and Co(II) ions from aqueous systems in a batch system. The adsorbents were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and Brunauer- Emmett-Teller (BET) analyses. The behavior of swelling kinetics was also studied. The effect of several adsorption parameters including CeO₂ and Fe₃O₄ contents, initial pH, contact time, initial Cr(VI) and Co(II) concentration, and temperature on the adsorption capacity was studied. The double exponential model revealed a better fit with the kinetic data of Cr(VI) and Co(II) ions. The Cr(VI) and Co(II) adsorption process well fitted the Langmuir model. The maximum adsorption capacities estimated from Langmuir isotherm model were 315.4 and 260.6 mg/g for Cr(VI) and Co(II) ions, respectively. Also, thermodynamic parameters were used to distinguish the nature of Cr(VI) and Co(II) adsorption. The reusability of CS/ceria/Fe₃O₄ nano-composite was evaluated with stripping agents of 0.1 M NaOH and 0.1 M HNO₃. Finally, the evaluation of Cr(VI)-Co(II) coexisting system confirmed that the presence of Co(II) ions played an inhibitor role on the Cr(VI) adsorption.

A Hydrothermal Synthesis of Fe3O4@C Hybrid Nanoparticle and Magnetic Adsorptive Performance to Remove Heavy Metal Ions in Aqueous Solution

Advanced core-shelled material with a high specific area has been considered as an effective material to remove heavy metal from aqueous solutions. A core-shelled Fe3O4@C hybrid nanoparticle aggregates with environmental-friendly channel in the study. Moreover, the higher exposure of adsorption sites can be achieved for the special configuration that higher Brunauer-Emmet-Teller (BET) surface area reaches up to 238.18 m2 g-1. Thus, a more efficiently heavy metal ion removal is obtained, Pb (II), Cd (II), Cu (II), and Cr (VI) up to 100, 99.2, 96.6, and 94.8%, respectively. In addition, the products are easy to be separated from the aqueous solutions after adsorption, due to the relative large submicrometer size and the enhanced external magnetic fields introduced by the iron-based cores. We provide an ideal mode to remove heavy metal ions using core-shelled Fe3O4@C under the water treatment condition. A new approach is clarified that core-shell nano/micro-functional materials can be synthesized well on large scales which are used in many fields such as environmental remediation, catalyst, and energy.