The efficient removal of bisphenol A from aqueous solution using an assembled nanocomposite of zero-valent iron nanoparticles/graphene oxide/copper: Adsorption isotherms, kinetic, and thermodynamic studies

Green synthesized hydroxyapatite for efficient immobilization of cadmium in weakly alkaline environment

The development of cost-effective passivators for the remediation of heavy metal-contaminated soils has been a research hotspot and an unsolved challenge. Herein, a novel hydroxyapatite (GSCH) was synthesized by co-precipitating distiller effluent-derived Ca with (NH₄)₂HPO₄ using straw-derived dissolved organic matter (S-DOM) as the dispersant. Batch adsorption experiments and soil incubation tests were performed to assess the immobilization efficiency of GSCH for Cd in weakly alkaline environments. As a result, GSCH showed an excellent adsorption efficiency to Cd with a maximum adsorption amount of ∼222 mg g^-1, which was fairly competitive compared to other similar previously materials reported. The kinetic data indicated that the adsorption of Cd on GSCH was a chemical and irreversible process, while the thermodynamic data revealed a spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption process. Based on mechanism analysis, both physisorption (e.g., electrostatic attraction and pore filling) and chemisorption (e.g., ion exchange and complexation) were responsible for Cd adsorption on GSCH. Particularly, the incorporated S-DOM and hydroxyapatite phase in GSCH acted synergistically in the adsorption process. The incubation results showed that GSCH application could significantly reduce the bioavailability, phytoavailability and bioaccessibility of Cd in soil by 48.4%-57.8%, 20.4%-28.6% and 12.6%-24.0%, respectively. Moreover, GSCH application also improved soil bacterial communities and enhanced soil nutrient availability. Overall, this is the first study to demonstrate the potential application value of GSCH in Cd immobilization, providing promising insights into the development of green and cost-effective hydroxyapatite-based passivators for the remediation of heavy metal-contaminated soils.

Graphene-based materials for effective adsorption of organic and inorganic pollutants: A critical and comprehensive review

Water scarcity has been felt in many countries and will become a critical issue in the coming years. The release of toxic organic and inorganic contaminants from different anthropogenic activities, like mining, agriculture, industries, and domestic households, enters the natural waterbody and pollutes them. Keeping this in view in combating the environmental crises, removing pollutants from wastewater is one of the ongoing environmental challenges. Adsorption technology is an economical, fast, and efficient physicochemical method for removing both organic and inorganic pollutants, even at low concentrations. In the last decade, graphene and its composite materials have become the center of attraction for numerous applications, including wastewater treatment, due to the large surface area, highly active surface, and exclusive physicochemical properties, which make them potential adsorbents with unique physicochemical properties, like low density, chemical strength, structural variability, and the possibility of large-scale fabrications. This review article provides a thorough summary/critical appraisal of the published literature on graphene-, GO-, and rGO-based adsorbents for the removal of organic and inorganic pollutants from wastewater. The synthesis methods, experimental parameters, adsorption behaviors, isotherms, kinetics, thermodynamics, mechanisms, and the performance of the regeneration-desorption processes of these substances are scrutinized. Finally, the research challenges, limitations, and future research studies are also discussed. Certainly, this review article will benefit the research community by getting substantial information on suitable techniques for synthesizing such adsorbents and utilizing them in water treatment and designing water treatment systems.

Discussion on the thermodynamic calculation by distribution constant in Journal of Contaminant Hydrology 243 (2021) 103906

This comment discussed the calculation of thermodynamic parameters about the paper published in Journal of Contaminant Hydrology 243 (2021) 103906. Despite the paper's novelty and innovation, the distribution constant (K_d) with a dimension of L/mg is not the standard equilibrium constant (K^o), therefore, it cannot be used to calculate the thermodynamic parameters. By analyzing the incorrect results and providing the reasonable method for calculating the thermodynamic parameters，this comment is helpful to understand the calculation principle of thermodynamic parameters by the distribution constant and avoid the misuse of incorrect formulas.

Comment on the calculation of equilibrium constant and thermodynamic parameters by the distribution coefficient in Environmental Research 203 (2022) 111814

This comment discussed the calculation of equilibrium constant and thermodynamic parameters in the paper of Kayalvizhi et al. (2022). This paper is of high academic value, however, there are some calculation and quotation errrors. The equilibrium constant K evolved from the distribution coefficient has a dimension of L/g, which is not the standard equilibrium constant, therefore, it cannot be used to calculate the thermodynamic parameters. This comment firstly analyzed the calculation errors made by Kayalvizhi et al. (2022), then established the relationship between distribution coefficient and standard equilibirum constant, and recalculated the thermodynamic parameters by using the correct distribution coefficient equation. As a research paper, authors not only provide the originality and novelty, but also give its correct results. This comment can bring to the attention of readers, authors, editors and reviewers about the thermodynamic calculation. At the same time, it is helpful to avoid the misuse and propagation of the incorrect equation in the area of adsorption thermodynamics.