Surface complexation modeling of adsorption of Cd(II) on graphene oxides

Ultrasonic-assisted synthesis of CaCu3Ti4O12/reduced graphene oxide composites for enhanced photocatalytic degradation of pharmaceutical products: Ibuprofen and Ciprofloxacin

The objective of this research is to create a highly effective approach for eliminating pollutants from the environment through the process of photocatalytic degradation. The study centers around the production of composites consisting of CaCu3Ti4O12 (CCTO) and reduced graphene oxide (rGO) using an ultrasonic-assisted method, with a focus on their capacity to degrade ibuprofen (IBF) and ciprofloxacin (CIP) via photodegradation. The impact of rGO on the structure, morphology, and optical properties of CCTO was inspected using XRD, FTIR, Raman, FESEM, XPS, BET, and UV-Vis. Morphology characterization showed that rGO particles were dispersed within the CCTO matrix without any specific chemical interaction between CCTO and C in the rGO. The BET analysis revealed that with increasing the amount of rGO in the composite, the specific surface area significantly increased compared to the CCTO standalone. Besides, increasing rGO resulted in a reduction in the optical bandgap energy to around 2.09 eV, makes it highly promising photocatalyst for environmental applications. The photodegradation of IBF and CIP was monitored using visible light irradiation. The results revealed that both components were degraded above 97% after 60 min. The photocatalyst showed an excellent reusability performance with a slight decrease after five runs to 93% photodegradation efficiency.

Effects of Carbonaceous Materials with Different Structures on Cadmium Fractions and Microecology in Cadmium-Contaminated Soils

Carbonaceous materials have proved to be effective in cadmium remediation, but their influences on soil microecology have not been studied well. Taking the structural differences and the maintenance of soil health as the entry point, we chose graphene (G), multi-walled carbon nanotubes (MWCNTs), and wetland plant-based biochar (ZBC) as natural and engineered carbonaceous materials to explore their effects on Cd fractions, nutrients, enzyme activities, and microbial communities in soils. The results showed that ZBC had stronger electronegativity and more oxygen-containing functional groups, which were related to its better performance in reducing soil acid-extractable cadmium (EX-Cd) among the three materials, with a reduction rate of 2.83-9.44%. Additionally, ZBC had greater positive effects in terms of improving soil properties, nutrients, and enzyme activities. Redundancy analysis and correlation analysis showed that ZBC could increase the content of organic matter and available potassium, enhance the activity of urease and sucrase, and regulate individual bacterial abundance, thereby reducing soil EX-Cd. Three carbonaceous materials could maintain the diversity of soil microorganisms and the stability of the microbial community structures to a certain extent, except for the high-dose application of ZBC. In conclusion, ZBC could better immobilize Cd and maintain soil health in a short period of time.

Superhigh Adsorption of Cadmium(II) Ions onto Surface Modified Nano Zerovalent Iron Composite (CNS-nZVI): Characterization, Adsorption Kinetics and Isotherm Studies

The efficiency of surface modified nanoscale zerovalent iron (nZVI) composite by cashew nut shell (CNS) was tested for the removal of cadmium ions from the aqueous solutions. 2 g/l CNS-nZVI was efficient for 98% removal. The adsorption capacity was 35.58 mg/g. The Freundlich isotherm (R2 = 0.9769) and the pseudo-second order adsorption kinetics data fitted well. This proved CNS-nZVI has a high removal efficiency for Cd(II) from aqueous solutions.

Potential environmental applications of MXenes: A critical review

Various environmental pollutants (e.g., air, water and solid pollutants) are discharged into environments with the rapid development of industrializations, which is presently at the forefront of global attention. The high efficient removal of these environmental pollutants is of important concern due to their potential threat to human health and eco-diversity. Advanced nanomaterials may play an important role in the elimination of pollutants from environmental media. MXenes as the new intriguing class of graphene-like 2D transition metal carbides and/or carbonitrides have been widely used in energy storage, environmental remediation benefitting from exceptional structural properties such as highly active sites, high chemical stability, hydrophilicity, large interlayer spacing, huge specific surface area, superior sorption-reduction capacity. However, the comprehensive investigation concerning the removal of various environmental pollutants on MXenes is yet not available up to date. In this review, we summarized the synthesis and properties of MXenes to demonstrate the key roles in ameliorating their adsorption performance; then the recent advances and achievements in environmental application of MXenes on the removal of gases, organics, heavy metals and radionuclides were comprehensively reviewed in details; Finally, the formidable challenges and further perspectives regarding utilizing MXene in environmental remediation were proposed. Hopefully, this review can provide the useful information for environmental scientists and material engineers on designing versatile MXenes in actual environmental applications.

Efficient adsorption of Cd2+ from aqueous solution using metakaolin geopolymers

In this study, geopolymers were prepared using metakaolin (MK) raw material under different alkali activator moduli (SiO₂/Na₂O = 0.8, 1.2, 1.6, 2.0 M ratio) in order to analyze their capacity and mechanism for adsorbing cadmium (Cd²⁺) from solution. Instrumental analyses including X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared (FTIR), and Brunauer-Emmett-Teller (BET) were performed to examine the mineralogical features of the MK and geopolymers before and after Cd²⁺ adsorption. The effect of initial pH, temperature, contact time, and initial concentration on Cd adsorption performance was studied to obtain the equilibrium isotherm. Kinetic data of the geopolymers fitted the pseudo-second-order kinetic model well. Moreover, the adsorption equilibrium data of Cd²⁺ adsorbed by the geopolymers fitted the Langmuir model better than the Freundlich model. The result shows that chemisorption dominates Cd²⁺ adsorption by geopolymers and that the adsorption capacity differs when prepared using different alkali-activated modulus agents. The geopolymer prepared using an alkali activator modulus of 0.8 M (molar ratio) exhibited the best Cd²⁺ adsorption performance with a maximum adsorption capacity of 70.3 mg g^-1. The removal rate of Cd²⁺ by geopolymer still remained above 85% after five round of recycling.

Exfoliation of Titanium Aluminum Carbide (211 MAX Phase) to Form Nanofibers and Two-Dimensional Nanosheets and Their Application in Aqueous-Phase Cadmium Sequestration

A green approach was adopted to exfoliate a Ti₂AlC MAX phase. The exfoliated nanostructures (Alk-Ti₂C_fibr and Alk-Ti₂C_sheet) with exceptional mechanical, thermal, and water stabilites, as well as abundant oxygenated active binding sites, were synthesized via a controlled hydrothermal treatment in an alkaline environment. The successful synthesis of nanofibers and sheetlike nanostructures was inferred with scanning electron microscopy and X-ray diffraction analyses. Field emission scanning electron microscopy, field-emission transmission electron microscopy, Raman spectroscopy, Brunauer-Emmett-Teller surface area, ζ-potential analyses, and X-ray photoelectron spectroscopy were utilized to investigate the material's characteristics and its structural changes after metal ion adsorption. Heavy metal ion adsorption of the synthesized nanostructures was assessed in batch tests based on Cd²⁺ ion sequestration; the maximum adsorption capacity for Cd²⁺ was 325.89 mg/g, which is among the highest values reported for similar materials such as graphene oxide and its derivatives. The detailed quantitative investigation confirmed the interaction of hydroxyl groups with Cd²⁺ ions by electrostatic interactions, adsorption-coupled oxidation, and complex formation. Owing to their unique structure, high porosity, large specific surface area, and oxygenated functional groups, Alk-Ti₂C_sheet nanosheets were highly time-efficient for Cd²⁺ removal. Moreover, Alk-Ti₂C_fibr and Alk-Ti₂C_sheet nanostructures were tested for simulated groundwater, showing that synthesized nanostructures were capable for removing Cd²⁺ ions at the ppb level. The results obtained from this study suggested that nanostructures synthesized using this route could provide a new approach to prepare and exfoliate additional MAX phases for the removal of heavy metal ions and other pollutants in the environment.

The adsorption of phosphate using a magnesia-pullulan composite: kinetics, equilibrium, and column tests

A magnesia-pullulan (MgOP) composite has been developed to remove phosphate from a synthetic solution. In the present study, the removal of phosphate by MgOP was evaluated in both a batch and dynamic system. The batch experiments investigated the initial pH effect on the phosphate removal efficiency from pH 3 to 12 and the effect of co-existing anions. In addition, the adsorption isotherms, thermodynamics, and kinetics were also investigated. The results from the batch experiments indicate that MgOP has encouraging performance for the adsorption of phosphate, while the initial pH value (3-12) had a negligible influence on the phosphate removal efficiency. Analysis of the adsorption thermodynamics demonstrated that the phosphate removal process was endothermic and spontaneous. Investigations into the dynamics of the phosphate removal process were carried out using a fixed bed of MgOP, and the resulting breakthrough curves were used to describe the column phosphate adsorption process at various bed masses, volumetric flow rates, influent phosphate concentrations, reaction temperatures, and inlet pH values. The results suggest that the adsorption of phosphate on MgOP was improved using an increased bed mass, while the reaction temperature did not significantly affect the performance of the MgOP bed during the phosphate removal process. Furthermore, higher influent phosphate concentrations were beneficial towards increasing the column adsorption capacity for phosphate. Several mathematic models, including the Adams-Bohart, Wolboska, Yoon-Nelson, and Thomas models, were employed to fit the fixed-bed data. In addition, the effluent concentration of magnesium ions was measured and the regeneration of MgOP investigated.

Adsorption of Cd(II) in water by mesoporous ceramic functional nanomaterials

Mesoporous ceramic functional nanomaterials (MCFN) is a self-assembled environmental adsorbent with a monolayer molecular which is widely used in the treatment of industrial wastewater and contaminated soil. This work aimed to study the relationship between the adsorption behaviour of Cd(II) by MCFN and contact time, initial concentration, MCFN dosage, pH, oscillation rate and temperature through a batch adsorption method. The adsorption kinetic and isotherm behaviours were well described by the pseudo-second-order and Langmuir models. The batch characterization technique revealed that MCFN had several oxygen-containing functional groups. Using Langmuir model, the maximum adsorption capacity of MCFN for Cd(II) was 97.09 mg g-1 at pH 6, 25°C, dosage of 0.2 g and contact time of 180 min. Thermodynamic study indicated that the present adsorption process was feasible, spontaneous and exothermic at the temperature range of 25-55°C. The results of this study provide an important enlightenment for Cd removal or preconcentration of porous ceramic nanomaterial adsorbents for environmental applications.

Enhanced Adsorption of Zn(II) onto Graphene Oxides Investigated Using Batch and Modeling Techniques

Graphene oxide (GO) was synthesized and employed as an adsorbent for Zn(II) removal from an aqueous solution. The adsorption isotherms showed that Zn(II) adsorption can be better described using the Freundlich model than the Langmuir model. The maximum adsorption capacity of Zn(II) on GO determined using the Langmuir model at pH 7.0 and 293 K was 208.33 mg/g. The calculation of thermodynamic parameters revealed that the process of Zn(II) adsorption on GO was chemisorptions, endothermic, and spontaneous. Kinetic studies indicated that the pseudo-second-order kinetic model showed a better simulation of Zn(II) adsorption than the pseudo-first-order kinetic model. On the basis of surface complexation modeling, the double layer model provided a satisfactory prediction of Zn(II) by inner-sphere surface complexes (for example, SOZn⁺ and SOZnOH species), indicating that the interaction mechanism between Zn(II) and GO was mainly inner-sphere complexation. In terms of reusability, GO could maintain 92.23% of its initial capability after six cycles. These findings indicated that GO was a promising candidate for the immobilization and preconcentration of Zn(II) from aqueous solutions.

Adsorption and co-adsorption of graphene oxide and Ni(II) on iron oxides: A spectroscopic and microscopic investigation

Graphene oxide (GO) may strongly interact with toxic metal ions and mineral particles upon release into the soil environment. We evaluated the mutual effects between GO and Ni (Ni(II)) with regard to their adsorption and co-adsorption on two minerals (goethite and hematite) in aqueous phase. Results indicated that GO and Ni could mutually facilitate the adsorption of each other on both goethite and hematite over a wide pH range. Addition of Ni promoted GO co-adsorption mainly due to the increased positive charge of minerals and cation-π interactions, while the presence of GO enhanced Ni co-adsorption predominantly due to neutralization of positive charge and strong interaction with oxygen-containing functional groups on adsorbed GO. Increasing adsorption of GO and Ni on minerals as they coexist may thus reduce their mobility in soil. Extended X-ray absorption fine structure (EXAFS) spectroscopy data revealed that GO altered the microstructure of Ni on minerals, i.e., Ni formed edge-sharing surface species (at R_Ni-Fe∼3.2 Å) without GO, while a GO-bridging ternary surface complexes (at R_Ni-C∼2.49 Å and R_Ni-Fe∼4.23 Å) was formed with GO. These findings improved the understanding of potential fate and toxicity of GO as well as the partitioning processes of Ni ions in aquatic and soil environments.

Implication of graphene oxide in Cd-contaminated soil: A case study of bacterial communities

The application of graphene oxide (GO) has attracted increasing concerns in the past decade regarding its environmental impacts, except for the impact of GO on a metal-contaminated soil system, due to its special properties. In the present work, the effects of GO on the migration and transformation of heavy metals and soil bacterial communities in Cd-contaminant soil were systematically evaluated. Soil samples were exposed to different doses of GO (0, 1, and 2 g kg^-1) over 60 days. The Community Bureau of Reference (BCR) sequential extraction procedure was used to reflect the interaction between GO and Cd. Several microbial parameters, including enzyme activities and bacterial community structure, were measured to determine the impacts of GO on polluted soil microbial communities. It was shown that Cd was immobilized by GO throughout the entire exposure period. Interestingly, the structure of the bacterial community changed. The relative abundance of the major bacterial phyla (e.g., Acidobacteria and Actinobacteria) increased, which was possibly attributed to the reduced toxicity of Cd in the presence of GO. However, GO exerted an adverse influence on the relative abundance of some phyla (e.g., WD272 and TM6). The diversity of bacterial communities was slightly restricted. The functional bacteria related to carbon and the nitrogen cycling were also affected, which, consequently, may influence the nutrient cycling in soil.

An X-ray absorption fine structure spectroscopy study of metal sorption to graphene oxide

Remediation and prevention of environmental contamination by toxic metals is an ongoing issue. Additionally, improving water filtration systems is necessary to prevent toxic metals from circulating through the water supply. Graphene oxide (GO) is a highly sorptive material for a variety of heavy metals under different ionic strength conditions over a wide pH range, making it a promising candidate for use in metal adsorption from contaminated sites or in filtration systems. We present X-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Cd (II), U(VI) and Pb(II) ions onto multi-layered graphene oxide (MLGO). This study shows that the binding environment of each metal onto the MLGO is unique, with different behaviors governing the sorption as a function of pH. For Cd sorption to MLGO, the same mechanism of electrostatic attraction between the MLGO and the Cd⁺² ions surrounded by water molecules prevails over the entire pH range studied. The U(VI), present in solution as the uranyl ion, shows only subtle changes as a function of pH, likely due to the varied speciation of uranium in solution. The adsorption of the U to the MLGO is through a covalent, inner-sphere bond. The only metal from this study where the dominant adsorption mechanism to the MLGO changes with pH is Pb. In this case, under lower pH conditions, Pb is bound onto the MLGO through dominantly outer-sphere, electrostatic adsorption, while under higher pH conditions, the bonding changes to be dominated by inner-sphere, covalent adsorption. Since each of the metals in this study show unique binding properties, it is possible that MLGO could be engineered to effectively adsorb specific metal ions from solution and optimize environmental remediation or filtration for each metal.

Chitin Adsorbents for Toxic Metals: A Review

Wastewater treatment is still a critical issue all over the world. Among examined methods for the decontamination of wastewaters, adsorption is a promising, cheap, environmentally friendly and efficient procedure. There are various types of adsorbents that have been used to remove different pollutants such as agricultural waste, compost, nanomaterials, algae, etc., Chitin (poly-β-(1,4)-N-acetyl-d-glucosamine) is the second most abundant natural biopolymer and it has attracted scientific attention as an inexpensive adsorbent for toxic metals. This review article provides information about the use of chitin as an adsorbent. A list of chitin adsorbents with maximum adsorption capacity and the best isotherm and kinetic fitting models are provided. Moreover, thermodynamic studies, regeneration studies, the mechanism of adsorption and the experimental conditions are also discussed in depth.

Functionalization of 4-aminothiophenol and 3-aminopropyltriethoxysilane with graphene oxide for potential dye and copper removal

In this work, 4-aminothiophenol and 3-aminopropyltriethoxysilane were firstly used to functionalize graphene oxide (GO) in order to promote the sorption efficiencies of methylene blue (MB) and copper (Cu(2+)). Characterization experiments illustrated that sulfydryl group (SH) and amino group (NH2) were existed onto 4-aminothiophenol modified GO (GO-SH) and 3-aminopropyltriethoxysilane modified GO (GO-N), respectively. Adsorption isotherm results showed that the maximum adsorption capacities of MB by GO-SH and GO-N were 763.30 and 676.22mg/g, which was much higher than original GO 455.95mg/g. For Cu(2+) adsorption, the maximum adsorption capacities by GO-SH and GO-N were 99.17 and 103.28mg/g, suggesting that the engineered GO exhibited greater Cu(2+) sorption ability than original GO 32.91mg/g. Both MB and Cu(2+) removal rates increased with pH and adsorbent dosage increased, while the sorption rates weakly reduced with increasing ionic strength. The modification by SH and NH2 would not only increase the sorption sites, but also cause chelation with heavy metals, and thus improving the sorption capacities of MB and Cu(2+).

Effect of Microbes on the Adsorption of Naphthalene by Graphene Oxide

The adsorption of naphthalene on graphene oxide (GO) nanosheets in presence of Paecilomyces cateniannulatus (P. cateniannulatus) was conducted by the batch techniques. The morphology and nanostructure of GO were characterized by SEM, TEM, FTIR, XPS, and Raman. The adsorption kinetics indicated that the adsorption of naphthalene on GO and GO + P. catenlannulatus can be satisfactorily fitted pseudo-first-order and pseudo-second-order kinetic model, respectively. P. catenlannulatus inhibited the adsorption of naphthalene on GO at pH<4.0, whereas the increased adsorption was observed at pH>4.0. The adsorption of naphthalene on GO and GO + P. catenlannulatus can be better fitted by Langmuir and Freundlich model, respectively. The change in the conformation of GO was responsible to the increased adsorption of naphthalene by SEM and TEM images. According to FTIR analysis, naphthalene was absorbed by the oxygen-containing functional groups of GO, especially for –COOH. The finding in the study provides the implication for the preconcentration and removal of polycyclic aromatic hydrocarbons from environment cleanup applications.