Fe-O-Zr in MOF for effective photo-Fenton Bisphenol A degradation: Boosting mechanism of electronic transmission

An anthraquinone-based bismuth-iron metal-organic framework as an efficient photoanode in photoelectrochemical cells

Metal-organic frameworks (MOFs) are appealing candidate materials to design new photoelectrodes for use in solar energy conversion because of their modular nature and chemical versatility. However, to date there are few examples of MOFs that can be directly used as photoelectrodes, for which they must be able to afford charge separation upon light absorption, and promote the catalytic dissociation of water molecules, while maintaining structural integrity. Here, we have explored the use of the organic linker anthraquinone-2, 6-disulfonate (2, 6-AQDS) for the preparation of MOFs to be used as photoanodes. Thus, the reaction of 2, 6-AQDS with Bi(iii) or a combination of Bi(iii) and Fe(iii) resulted in two new MOFs, BiPF-10 and BiFePF-15, respectively. They display similar structural features, where the metal elements are disposed in inorganic-layer building units, which are pillared by the organic linkers by coordination bonds through the sulfonic acid groups. We show that the introduction of iron in the structure plays a crucial role for the practical use of the MOFs as a robust photoelectrode in a photoelectrochemical cell, producing as much as 1.23 mmol H2 cm-2 with the use of BiFePF-15 as photoanode. By means of time-resolved and electrochemical impedance spectroscopic studies we have been able to unravel the charge transfer mechanism, which involves the formation of a radical intermediate species, exhibiting a longer-lived lifetime by the presence of the iron-oxo clusters in BiFePF-15 to reduce the charge transfer resistance.

Strategies to improve adsorption and photocatalytic performance of metal-organic frameworks (MOFs) for perfluoroalkyl and polyfluoroalkyl substances (PFASs) removal from water: A review

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent a category of persistent and hazardous organic pollutants extensively prevalent across aquatic environments. The combination of adsorption and photocatalytic degradation has been identified as an effective approach for removing trace amounts of PFASs from water. Among the various materials explored for this purpose, metal-organic frameworks (MOFs) have structural solid tunability, and suitable modification methods could endow them with rich adsorption capabilities and excellent photocatalytic performance, which has potential for applications involving the treatment of trace, multi-chain-length PFASs in water. The research within this realm is currently in its nascent phase, and a holistic knowledge of modification methods can provide a comprehensive framework for future studies. Therefore, this review intends to (1) summarize the mechanism underlying the adsorption and photocatalytic removal of PFASs by MOFs; (2) present various modification methods aimed at enhancing the adsorption and photocatalytic performance of MOFs in alignment with the goal mentioned above; (3) provide an outlook on the prospects of utilizing MOFs for PFASs removal based on current trends and data. Ultimately, the findings from these studies will contribute to advancing knowledge in this area and facilitate the development of effective strategies for addressing PFASs contamination in water systems.

Construction of urchin-like core-shell Fe/Fe2O3@UiO-66 hybrid for effective tetracycline reduction and photocatalytic oxidation

Although Fe/Fe2O3 has potential application compared with nanoscale zero-valent iron (nZVI), its smooth structure largely limits the catalytic performance. To address this challenge, we innovatively constructed highly efficient composite Fe/Fe2O3@UiO-66 via employing an urchin-like core-shell structure of Fe/Fe2O3 onto UiO-66 through a facile ion exchange precipitation method without inert gas protection. The characterization results show the urchin-like core-shell configuration can extend the life span of Fe0 and produce more active sites. Besides, the absorption spectrum is broadened by Fe2O3 which has narrow band gap and the high-efficiency separation of photogenerated electron-hole pairs is obtained with the load of Fe/Fe2O3. Moreover, Two-parameter pseudo-first-order decay model fits well with the reduction and adsorption of composites in the dark reaction, and a plausible pathway for tetracycline (TC) degradation is also proposed. The findings of this research provide a promising method for promoting the catalytic properties of MOF-based materials and Fe/Fe2O3.

Ultrafast short-range catalytic pathway modified peroxymonosulfate activation over CuO with surface oxygen defects for tetracycline hydrochloride degradation

The presence of antibiotics in water bodies seriously threatens the ecosystem and human health. Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS), an effective method to remove antibiotics, have a bottleneck problem that the low oxidant utilization is attributed to the hindered electron transfer between metal oxides and peroxides. Here, CuO with rich oxygen vacancies (OVs), MSCuO-300, was synthesized to efficiently degrade tetracycline hydrochloride (TTCH) (k = 0.095 min^-1). The dominant role of direct adsorption and activation of OVs and its regulated Cu-O, rather than surface hydroxyl adsorption, mediated a short-range catalytic pathway. The shortened catalytic pathway between active sites and PMS accelerated the charge transfer at the interface, which promoted PMS activation. Compared with Cu_xO-500 and Commercial CuO, the activation rate of PMS was increased by 11.97, and 12.64 times, respectively. OVs contributed to the production of ¹O₂ and O₂^•-, the main active species. In addition, MSCuO-300/PMS showed excellent adaptability to real water parameters, such as pH (3-11), anions, and continuous reactor maintained for 168 h. This study provides a successful case for the purification of antibiotic-containing wastewater in the design of efficient catalysts by oxygen defect strategies.

Carbonate and bicarbonate ions impacts on the reactivity of ferrate(VI) for 3,4-dichlorophenol removal

Carbonate and bicarbonate ions are common constituents found in wastewater and natural water matrices, and their impacts on the reactivity of ferrate(VI) (Fe(VI)) with 3,4-dichlorophenol (3,4-DCP) were investigated by determining second-order rate constants of 3,4-DCP removal by Fe(VI) in the presence of CO₃^2- and/or HCO₃^-. The second-order rate constants decreased from 41.75 to 7.04 M^-1 s^-1 with an increase of [CO₃^2-] from 0 to 2.0 mM, indicating that CO₃^2- exhibits an inhibitory effect on 3,4-DCP removal kinetics, and experiments on pH effect, radical quenching, and Fe(VI) stability were conducted to explore possible reasons for its effect. Under identical pH conditions, the rate constant in NaOH medium was always higher than in Na₂CO₃ medium, suggesting that the inhibitory effect partially comes from an increase in alkalinity. Furthermore, the scavenging of hydroxyl radical by carbonate ion also contributed to the inhibitory effect of CO₃^2-. On the other hand, the enhancement effect of CO₃^2- depending on the increase in Fe(VI) stability was found, but did not exceed its inhibitory effect. In addition, 3,4-DCP removal kinetics was not affected by HCO₃^-, while synergistically inhibited by CO₃^2-/HCO₃^-. Moreover, 3,4-DCP removal efficiency was substantially suppressed in the presence of CO₃^2-, while the slight enhancement effect of HCO₃^- and the synergistic inhibitory effect of CO₃^2-/HCO₃^- were observed. The experimental results clearly demonstrated that carbonate and bicarbonate ions play an important role in the process of 3,4-DCP removal by Fe(VI) and should not be considered only as scavengers.

Visible-light-driven iron-based heterogeneous photo-Fenton catalysts for wastewater decontamination: A review of recent advances

Visible-light-driven heterogeneous photo-Fenton process has emerged as the most promising Fenton-derived technology for wastewater decontamination, owing to its prominent superiorities including the potential utilization of clean energy (solar light), and acceleration of ≡Fe(II)/≡Fe(III) dynamic cycle. As the core constituent, catalysts play a pivotal role in the photocatalytic activation of H₂O₂ to yield reactive oxidative species (ROS). To date, all types of iron-based heterogeneous photo-Fenton catalysts (Fe-HPFCs) have been extensively reported by the scientific community, and exhibited satisfactory catalytic performance towards pollutants decomposition, sometimes even exceeding the homogeneous counterparts (Fe(II)/H₂O₂). However, the relevant reviews on Fe-HPFCs, especially from the viewpoint of catalyst-self design are extremely limited. Therefore, this state-of-the-art review focuses on the available Fe-HPFCs in literatures, and gives their classification based on their self-characteristics and modification strategies for the first time. Two classes of representative Fe-HPFCs, conventional inorganic semiconductors of Fe-containing minerals and newly emerging Fe-based metal-organic frameworks (Fe-MOFs) are comprehensively summarized. Moreover, three universal strategies including (i) transition metal (TMs) doping, (ii) construction of heterojunctions with other semiconductors or plasmonic materials, and (iii) combination with supporters were proposed to tackle their inherent defects, viz., inferior light-harvesting capacity, fast recombination of photogenerated carriers, slow mass transfer and low exposure and uneven dispersion of active sites. Lastly, a critical emphasis was also made on the challenges and prospects of Fe-HPFCs in wastewater treatment, providing valuable guidance to researchers for the reasonable construction of high-performance Fe-HPFCs.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Self-powered photoelectrochemical aptasensor based on AgInS2@Co/Ni-UiO-66@CDs photoelectrode for estradiosl detection

A self-powered photoelectrochemical (PEC) aptasensor was constructed to sensitively detect 17β-estradiol (E₂). Firstly, a reasonable AgInS₂@Co/Ni-UiO-66@Carbon Nanodots (CDs) photoelectrode with excellent photoelectrochemical performance was built by a simple two-step preparation method. The Co and Ni doping markedly improved the activity of UiO-66; the matched energy level of AgInS₂ and Co/Ni-UiO-66 promoted the separation of electron-hole pairs, and the coupling of CDs further enhanced the conductivity and light utilization. Therefore, a steady anode-photocurrent signal output was obtained in 0.0 V bias voltage, providing a reliable photoelectric translating platform for assembling a self-powered PEC aptasensor. The E₂-aptamer was adopted as a recognition unit to enhance the selectivity and sensitivity of the proposed aptasensor. The specific recognition reaction between E₂ and aptamer administering to a raised photocurrent signal and the concentration of E₂ was quantified by counting the fluctuation of the anode-photocurrent signal. The linear response range of the PEC aptasensor was 1.0 × 10^-5-10 nmol/L, and the detection limit (S/N = 3) was lower than 3.0 fmol/L under optimal conditions. The fabricated aptasensor exhibited admirable selectivity, high sensitivity, rapid response, and wide linear range, demonstrating an extensive application prospect for environmental endocrine disruptor detection.