The in situ catalytic oxidation of sulfamethoxazole via peroxydisufate activation operated in a NG/rGO/CNTs composite membrane filtration

Synergistic interface engineering in n-p-n type heterojunction Co3O4/MIL/Mn-STO with dual S-scheme multi-charge migration to enhance visible-light photocatalytic degradation of antibiotics

Constructing an effective multi-heterojunction photocatalyst with maximum charge carrier separation remains challenging. Herein, a high-efficient Co3O4/MIL-88A/Mn-SrTiO3 (Co3O4/MIL/Mn-STO) n-p-n heterojunction photocatalyst was successfully prepared by a simple hydrothermal method for the photodegradation of sulfamethoxazole (SMX). The combination of MIL and Co3O4/Mn-STO established an internal electric field and heterojunction, accelerating the separation of carriers, and thus improved photocatalytic performance. In the Co3O4/MIL/Mn-STO photocatalytic system, 95.5 % of SMX was degraded in 90 min. The photocatalytic kinetic removal rate of Co3O4/MIL/Mn-STO reached 0.0337 min-1, 8 times of Co3O4 (0.0041 min-1), 5.2 times of Mn-STO (0.0062 min-1), 4.6 times of MIL (0.0078 min-1), and 3.6 times of MIL/Mn-STO (0.0095 min-1). Remarkably, superoxide radicals (•O2-) and holes (h+) have been recognized as the main active species in the degradation process through reactive species elimination experiments and electron spin resonance (ESR) tests. The experimental and theoretical proved the in-built interfacial contact and synergistic effect between the photocatalyst accomplished with low bandgaps, high specific surface area, more reaction sites, high electron-hole pair separation, and maximum solar-light utilization. The molecular structure and possible degradation routes with intermediate products in the photocatalytic system were investigated using a liquid chromatography-mass spectrometer (LC-MS) and DFT calculations. This work provided new insight into the guidelines of rational design/growth of new multicomponent photocatalysts to remove antibiotics and other emerging contaminants in wastewater.

Metal-free graphene-based catalytic membranes for persulfate activation toward organic pollutant removal: a review

Owing to their ultrathin two-dimensional structure and efficient catalytic ability for persulfate activation, graphene-based nanocarbons exhibit considerable application potential in fabricating carbonaceous composite membranes for in situ catalytic oxidation to remove organic pollutants. This approach offers significant advantages over conventional batch systems. However, the relationships between the physicochemical properties of carbon mats and performance of graphene-based catalytic membranes in water purification remain ambiguous. Herein, we summarize the main mechanisms of in situ catalytic oxidation and the facile fabrication strategies of carbonaceous composite membranes. Different factors influencing the performance of graphene-based catalytic membranes are comprehensively discussed. The defective level, heteroatom doping, and stacking morphology of carbon mats and operational conditions during filtration play critical roles in the oxidative degradation of target pollutants. Long-term operation leads to the deterioration of catalytic activity and transmembrane pressure, especially in the complex water matrix. Finally, the present challenges and future perspectives are presented to improve the anti-fouling performance and catalytic stability of membranes and develop scalable fabrication methods to promote the engineering applications of in situ catalytic oxidation in real water purification.

Magnetic graphene oxide for methylene blue removal: adsorption performance and comparison of regeneration methods

A series of Fe₃O₄-graphene oxide (GO) composite materials (MGOs) with abundant surface area, rich oxygen-containing functional groups, and magnetic properties were prepared in a facile coprecipitation method and then employed for the adsorptive removal of methylene blue (MB) from water. The kinetic data were better fitted in the pseudo-second-order model than in the pseudo-first-order model, and the intraparticle diffusion model revealed the two-step diffusion process including diffusion in the boundary layer and in the porous structures. The maximum adsorption amounts of MB were calculated to be 37.5-108 mg/g at 25 °C and pH 9 using the Langmuir isotherm model. Thermodynamic study showed that the adsorption process was spontaneous, with ΔH° of 23.0-49.6 kJ/mol and ΔS° of 131-249 J∙mol^-1∙K^-1. The adsorption amount of MB increased with pH in the range of 4-10. Inorganic ions including Na⁺ and Ca²⁺ suppressed the adsorption of MB, and the more pronounced impact of Ca²⁺ was ascribed to its higher valence state. The cetyltrimethylammonium bromide (CTAB) surfactant showed a stronger inhibitory effect than Ca²⁺. The adsorption mechanism was proposed to be a combination of electrostatic interactions, hydrophobic adsorption, and electron donor-acceptor interactions. Two methods were used for the regeneration of spent MGO, and the results showed that the peroxomonosulfate (PMS) oxidation method was more favorable than the acid washing method, considering the better regeneration ability and lower amount of washing water used. Finally, the reaction mechanism of PMS oxidation was analyzed based on quenching tests and in situ open circuit potential measurements, which proved that OH and ¹O₂ played dominant roles and that the fine adsorption ability of MGO promoted the reaction between them and MB.

Carbonaceous composite membranes for peroxydisulfate activation to remove sulfamethoxazole in a real water matrix

In this study, we fabricated carbonaceous composite membranes by loading integrated mats of nitrogen-doped graphene, reduced graphene oxide, and carbon nanotubes (NG/rGO/CNTs) on a nylon microfiltration substrate and employed it for in-situ catalytic oxidation by activating peroxydisulfate (PDS) for the removal of sulfamethoxazole (SMX) in a real water matrix. The impact of coexisting organics on the performance of carbonaceous catalysis was investigated in the continuous filtration mode. Reusability testing and radical quenching experiments revealed that the non-radical pathways of surface-activated persulfate mainly contributed to SMX degradation. A stable SMX removal flux (r_SMX) of 22.15 mg m^-2·h^-1 was obtained in 24 h when tap water was filtered continuously under a low pressure of 1.78 bar and in a short contact time of 1.4 s, which was slightly lower than the r_SMX of 23.03 mg m^-2·h^-1 performed with deionized water as the control group. In addition, higher contents of protein-, fulvic acid-, and humic acid-like organics resulted in membrane fouling and significantly suppressed SMX removal during long-term filtration. Changes in the production of sulfate ions and the Raman spectra of carbon mats indicated that organics prevent the structural defects of the carbon matrix from participating in PDS activation. Moreover, NG/rGO/CNTs composite membranes coupled with activated persulfate oxidation exhibited good self-cleaning ability, because membrane fouling could be partly reversed by restoring filtration pressure during operation. This study provides a novel and effective oxidation strategy for efficient SMX removal in water purification, allowing the application of carbonaceous catalysis for the selective degradation of emerging contaminants.

Prussian blue modified CeO2 as a heterogeneous photo-Fenton-like catalyst for degradation of norfloxacin in water

The heterogeneous photo-Fenton-like process is emerging as a promising treatment of antibiotics-containing wastewater. The preparation of new efficient and stable catalysts is one of the research fields. A composite catalyst, prussian blue (PB) modified CeO₂ was prepared, characterized, and applied for photo-Fenton oxidation of norfloxacin (NOR) in this study. It was found that chemical doping of PB leaded to more oxygen vacancies and increased the surface area of CeO₂ obviously. PB/CeO₂ with more Ce³⁺ facilitated electron transfer between Fe³⁺/Fe²⁺ with Ce³⁺/Ce⁴⁺. PB could also improve the separation rate of photoexcited electron-hole pairs in CeO₂ nanostructures. When the doping ratio of PB and CeO₂ was 10%, PB/CeO₂ show the highest catalytic degradation ability and 88.93% of NOR could be degraded within 30 min. PB/CeO₂ composite showed well reactivity at the wide pH value range of 3-8. The reusable experiments and low iron dissolution with less than 1 mg/L indicated that PB/CeO₂ could be employed as an efficient heterogeneous photo-Fenton-like catalyst in organic contaminants degradation.