Molecular characteristics of dissolved organic matter regulate the binding and migration of tungsten in porous media

Tungsten (W) is an emerging contaminant that poses potential risks to both the environment and human health. While dissolved organic matter (DOM) can significantly influence the W's environmental behavior in natural aquifers, the mechanisms by which DOM's molecular structure and functional group diversity impact W binding and migration remain unclear. Using molecular weight-fractionated soil and sediment DOM (<1 kDa, 1-100 kDa, and 100 kDa-0.45 μm), this study systematically investigated the relationship between DOM molecular characteristics and tungstate (WO42-) binding properties using multiple spectroscopic methods, including FTIR, fluorescence spectroscopy and XPS. The migration behavior of WO42- in porous media was also investigated through quartz sand column experiments. Results revealed that approximately 75 % of W was controlled by DOM, with over 50 % binding to low molecular weight DOM (<1 kDa). Tungsten bound to medium-high molecular weight DOM (1-100 kDa, >100 kDa) showed a greater propensity for retention, with the >100 kDa fractions demonstrating stronger selective binding to W, exhibiting distribution coefficients (Kmd) of 6.11 L/g and 10.69 L/g, respectively. Further analysis indicated that W primarily binds with aromatic rings, phenolic hydroxyls, polysaccharides, and carboxyl groups in DOM, potentially affecting DOM structural stability and consequently influencing W migration characteristics. Free W migration in quartz sand was primarily controlled by Langmuir monolayer adsorption, leading to local enrichment (Da = 6.83, Rd = 86.98). When bound to DOM, W's migration ability significantly increased (Rd = 8-10), with adsorption shifting to a Freundlich multilayer model, primarily controlled by convective transport (Npe = 27-62> > 1.96), while adsorption effects weakened (Da ≈ 1). This study, for the first time, systematically reveals the regulatory mechanisms of DOM molecular characteristics on tungsten's environmental behavior. It offers crucial parameter support for constructing tungsten migration models and provides important guidance for tungsten pollution risk assessment and remediation strategies.

Construction of UiO-66-NH2 decorated by MoS2 QDs as photocatalyst for rapid and effective visible-light driven Cr(VI) reduction

The photoactive metal-organic frameworks (MOFs) are good candidates for photocatalysts, but the quick electron-hole pairs recombination has greatly restricted the photocatalytic ability of MOFs. To improve the photoactivity of MOFs, MOFs-based composite materials have been extensively studied. Here, we successfully integrated MoS2 quantum dots (QDs) with UiO-66-NH2 for the first time under hydrothermal conditions. The as-prepared MoS2 QDs/UiO-66-NH2 (MS-U) had good visible light response ability (absorption edge at 445 nm), and charge separation and transfer ability, which lays the foundation for the photocatalytic Cr(VI) reduction. Photocatalytic studies revealed that MoS2 QDs-5/UiO-66-NH2 (MS-U-5) had superior Cr(VI) reduction activity than pure MoS2 QDs and UiO-66-NH2. MS-U-5 could remove 98% Cr(VI) at pH= 2 with visible light irradiation for 20 min, which is the fastest visible light driven Cr(VI) reduction rate among the reported MOFs-based composite photocatalysts without the presence of any cocatalysts or scavengers as far as we know. Importantly, MS-U-5 could be reused at least three times. In the end, the possible electron transfer path and mechanism of Cr(VI) reduction was also investigated.

Recent Progress in the Development of MOF-Based Photocatalysts for the Photoreduction of Cr(VI)

There has been a direct correlation between the rate of industrial development and the spread of pollution on Earth, particularly in the last century. The organic and inorganic pollutants generated from industrial activities have created serious risks to human life and the environment. The concept of sustainability has emerged to tackle the environmental issues in developing chemical-based industries. However, pollutants have continued to be discharged to water resources, and finding appropriate techniques for the removal and remedy of wastewater is in high demand. Chromium is one of the high-risk heavy metals in industrial wastewaters that should be removed via physical adsorption and/or transformed into less hazardous chemicals. Photocatalysis as a sustainable process has received considerable attention as it utilizes sunlight irradiation to remedy Cr^(VI) via a cost-effective process. Numerous photocatalytic systems have been developed up to now, but metal-organic frameworks (MOFs) have gained growing attention because of their unique versatilities and facile structural modulations. A variety of MOF-based photocatalysts have been widely employed for the photoreduction of Cr^(VI). Here, we review the recent progress in the design of MOF photocatalysts and summarize their performance in photoreduction reactions.

A series of POM compounds constructed using a flexible ligand containing three coordination groups: electrocatalytic and photocatalytic reduction and amperometric detection of Cr(vi)

Four polyoxometalate-based compounds can be used as electrocatalysts and electrochemical sensors for amperometric detection of NO2− and Cr(VI), and also have the performance of photocatalytic reduction of Cr(VI).

The enhancement mechanism of ultra-active Ag3PO4 modified by tungsten and the effective degradation towards phenolic pollutants

A novel strategy of W modification was applied to overcome the disadvantages of Ag₃PO₄. Ultra-active Ag₃PO₄ with different W doping ratios were successfully synthesized by facile chemical precipitation method, among which 0.5%W-AP showed the best results. Meanwhile, the stability and yield were enhanced. XRD, Raman and ESR etc. were employed to investigate the morphology, structure and optical properties of samples. It was proved W⁶⁺ entered into the Ag₃PO₄ lattice, occupied the position of P⁵⁺ and doped in the form of WO₄^2-. The significant improvement of photocatalytic performance of W doped Ag₃PO₄ was attributed to the change of morphology, the decrease of particle size, the increase of crystallinity, the shrink of band gap energy and the reduction of photo-induced carriers recombination rate with W doping. The photocatalytic mechanism analysis showed h⁺ was the main oxidative species in the photocatalytic process, •O₂^- and •OH played minor roles. Under visible light irradiation, the impacts of the important operating parameters on the typical phenolic pollutants, phenol and bisphenol A, were evaluated with 0.5%W-AP. It was confirmed that 68% and 82% of phenol and bisphenol A were respectively degraded within 15 min and 40 min under optimized photocatalytic parameters: 0.4 g/L catalyst dosage, 20 mg/L pollutant concentration, pH 5.7 and 125 mW/cm² irradiation intensity, and the corresponding K' were 2.14 and 5.50 times of undoped samples. This work provides a new approach for effective degradation towards phenolic pollutants by Ag₃PO₄ with ultra-high photocatalytic activity, high applicability and enhanced stability and yield.

Facile fabrication of AgI/Sb2O3 heterojunction photocatalyst with enhanced visible-light driven photocatalytic performance for efficient degradation of organic pollutants in water

The construction of heterojunction is considered as a promising approach to designing highly effective visible-light driven photocatalysts. In this research, the AgI/Sb₂O₃ heterojunction photocatalyst was synthesized by a simple in situ deposition-precipitation procedure, which was supported by XPS results. Among the prepared samples, the 60% AgI/Sb₂O₃ samples exhibited the best ARG degradation ratio (98.3%) in 1 h under visible light irradiation, while the pure Sb₂O₃ and AgI exhibited almost none photocatalytic performance. The trapping experiments and EPR proved that the photo-generated ·O₂^- and ·OH made major contributions to the photocatalytic degradation of ARG by the 60% AgI/Sb₂O₃ samples. The enhanced photocatalytic performance of AgI/Sb₂O₃ heterojunction photocatalysts was ascribed to that the e^- produced in the CB of AgI would be transferred to the empty CB of Sb₂O₃, which could effectively promote separation of photo-induced carries. More importantly, the transfer of electrons from AgI to Sb₂O₃ would be in favor of restraining the reduction of Ag⁺ to Ag⁰ resulting in the good stability of heterojunction photocatalysts. The heterojunction photocatalyst provided in this work might be a prospective candidate for decontamination of water.