Efficient removal of antimonate from water by yttrium-based metal-organic framework: Adsorbent stability and adsorption mechanism investigation

Arsenic and antimony desorption in water treatment processes: Scaling up challenges with emerging adsorbents

The metalloids arsenic (As) and antimony (Sb) belong to the pnictogen group of the periodic table; they share many characteristics, including their toxic and carcinogenic properties; and rank as high-priority pollutants in the United States and the European Union. Adsorption is one of the most effective techniques for removing both elements and desorption, for further reuse, is a part of the process to make adsorption more sustainable and feasible. This review presents the current state of knowledge on arsenic and antimony desorption from exhausted adsorbents previously used in water treatment, that has been reported in the literature. The application of different types of eluents to desorb As and Sb and their desorption performance are described. The regeneration of saturated adsorbents and adsorbate recovery techniques are outlined, including the fate of spent media and possible alternatives for waste disposal of exhausted materials. Future research directions are discussed, as well as current issues including the lack of environmental impact analysis of emerging adsorbents.

Study of Barium Adsorption from Aqueous Solutions Using Copper Ferrite and Copper Ferrite/rGO Magnetic Adsorbents

The development of advanced materials for the removal of heavy metal ions is a never-ending quest of environmental remediation. In this study, a facile and cost-effective approach was employed to synthesize copper ferrite (CF) and copper ferrite/reduced graphene oxide (CG) by microwave assisted combustion method for potential removal of barium ions from aqueous medium. The physiochemical characterizations indicated the formation of magnetic nanocomposite with an average crystallite size of CF and CG is 32.4 and 30.3 nm and with specific surface area of 0.66 and 5.74 m2/g. The magnetic results possess multidomain microstructures with saturation magnetization of 37.11 and 33.84 emu/g for CF and CG. The adsorption studies prove that upon addition of rGO on the spherical spinel ferrite, the adsorption performance was greatly improved for CG nanocomposite when compared with the bare CF nanoparticles. The proposed magnetic adsorbent demonstrated a relatively high Ba2+ adsorption capacity of 161.6 mg·g-1 for CG nanocomposite when compared to 86.6 mg·g-1 for CF nanoparticles under optimum conditions ( $\text{pH}=7;T={25}^{°}\text{C}$ ). The pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich models were fitted to the kinetic data, the yielded $R^2$ value of 0.9993 (PSO) for CF and 0.9994 (PSO) for CG which is greater than the other two models, which signify that the adsorption process is chemisorption. Thermodynamic studies show that barium adsorption using CF and CG adsorbents is endothermic. The as-fabricated CuFe2O4/rGO nanocomposite represents a propitious candidate for the removal of heavy metal ions from aqueous solutions.

Modifying SnS2 With Carbon Quantum Dots to Improve Photocatalytic Performance for Cr(VI) Reduction

The photoreduction for hazardous Cr(VI) in industrial wastewater has been considered a "green" approach with low-cost and easy-to-go operation. SnS₂ is a promising narrow bandgap photocatalyst, but its low charge carrier separation efficiency should be solved first. In this work, N-doped carbon quantum dots (CQDs) were prepared and loaded onto SnS₂ nanoparticles via an in situ method. The resulting composite samples (NC@SnS₂) were characterized, and their photocatalytic performance was discussed. SnS₂ nanoparticles were obtained as hexagonal ones with a bandgap of 2.19 eV. The optimal doping level for NC@SnS₂ was citric acid: urea:SnS₂ = 1.2 mmol:1.8 mmol:3.0 mmol. It showed an average diameter of 40 nm and improved photocatalytic performance, compared to pure SnS₂, following a pseudo-first-order reaction with a kinetic rate constant of 0.1144 min^-1. Over 97% of Cr(VI) was photo-reduced after 30 min. It was confirmed that modification of SnS₂ with CQDs can not only improve the light-harvesting ability but also stimulate the charge separation, which therefore can enhance the photoreactivity of SnS₂ toward Cr(VI) reduction. The excellent stability of NC@SnS₂ indicates that it is promising to be practically used in industrial wastewater purification.