Microfiltration Membranes for the Removal of Bisphenol A from Aqueous Solution: Adsorption Behavior and Mechanism

Approaches for the Efficient Removal of Fluoride from Groundwater: A Comprehensive Review

Contamination of groundwater with fluoride represents a significant global issue, with high concentrations posing serious public health threats. While fluoride is a critical element in water, excessive levels can be detrimental to human health and potentially life-threatening. Addressing the challenge of removing fluoride from underground water sources via nanotechnological approaches is a pressing concern in environmental science. To collate relevant information, extensive literature searches were conducted across multiple databases, including Google Scholar, PubMed, Scopus, Web of Science, the American Chemical Society, Elsevier, Springer, and the Royal Society of Chemistry. VOS Viewer software version 1.6.20 was employed for a systematic review. This article delivers an exhaustive evaluation of various groundwater fluoride removal techniques, such as adsorption, membrane filtration, electrocoagulation, photocatalysis, and ion exchange. Among these, the application of nanoparticles emerges as a notable method. The article delves into nano-compounds, optimizing conditions for the fluoride removal process and benchmarking their efficacy against other techniques. Studies demonstrate that advanced nanotechnologies-owing to their rapid reaction times and potent oxidation capabilities-can remove fluoride effectively. The implementation of nanotechnologies in fluoride removal not only enhances water quality but also contributes to the safeguarding of human health.

Facile activation of natural calcium-rich sepiolite with oxalic acid for selective Pb(II) removal: Highly-efficient performance, mechanisms and site energy distribution

The design and development of adsorbents with high efficiency, selectivity, and economy for Pb(II) are essential to environmental governance and ecological safety. Herein, an oxalic acid (OA) activated natural sepiolite (nSEP) composite for highly efficient Pb(II) removal was prepared by a facile impregnation strategy. The OA activated nSEP nanocomposite (OA-nSEP) was characterized by various instrumental techniques and its adsorption performance towards Pb(II) was further evaluated through a series of static and dynamic experiments under various environmental conditions. Results revealed that OA reacted with the calcium impurities in nSEP to form calcium oxalate, causing mesoporous structure and larger specific surface area of OA-nSEP. The obtained OA-nSEP possessed super high Pb(II) adsorption capacities (858.4-1252 mg/g), which were much higher than that of most modified clays or conventional materials. The average adsorption site energy and the standard deviation of the site energy distribution were analyzed to investigate the strength of Pb(II) binding onto OA-nSEP and the adsorption site heterogeneity. Mechanism studies confirmed that oxalate groups exerted a primary role in the adsorption process. X-ray diffraction and X-ray photoelectron spectrometry (XPS) unveiled that the coordination of oxalate with Pb(II) and precipitation of lead oxalate was responsible for the high efficiency and selectivity. Distinguishing feature of high adsorption capacity, specific selective adsorption, abundant availability, and splendid reusability make the OA-nSEP a promising candidate for eliminating Pb(II) in practical scenarios.

Carboxyl-functionalized polyimides for efficient bisphenol A removal: Influence of wettability and porosity on adsorption capacity

Bisphenol A (BPA) removal from drinking water is greatly concerned for human and living things' safety. In this study, we synthesized three carboxyl-functionalized copolyimides and their homopolymer counterparts and evaluated their potential for removing BPA from an aqueous solution. The polymers were prepared via polycondensation reaction by reacting 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various ratios of 3,5-diaminobenzoic acid (DABA) and 3,5-diamino-2,4,6-trimethylbenzoic acid (TrMCA). The effect of porosity, hydrophilicity, and methyl group content on BPA adsorption capacity has been investigated systemically. 6FDA-DABA demonstrated the highest BPA adsorption capacity with maximum adsorption of 67 mg g^-1 and removal efficiency of approximately 90%. The anti-synergistic regime was observed between polymer porosity and hydrophilicity. As the content of the methyl group increases, the Brunauer-Emmett-Teller (BET) surface area increases, and the polymer hydrophilicity decreases, leading to a notable reduction in BPA adsorption capacity. The adsorption kinetics isotherms of BPA on 6FDA-based polyimides followed the pseudo-first-order kinetics, except for 6FDA-DABA, which was found to follow the pseudo-second-order. The BPA removal capacity was determined using both Langmuir and Freundlich isotherm models. The Langmuir model was more suitable than the Freundlich for the adsorption of BPA on the carboxyl-functionalized polyimides. To our knowledge, the prepared polyimides represent the first examples of utilizing polyimides for BPA removal. Investigating the structure/property relationship between polymers and their performance will pave the way to molecular engineering state-of-the-art polymer materials for efficient environmental remediation applications.