Simulated Sunlight Research Articles

Construction of ZnCo2O4/Ag3PO4 composite photocatalyst for enhanced photocatalytic performance

AbstractIn this study, ZnCo2O4/Ag3PO4 composite catalyst was prepared by the precipitation method, and their performance in the photocatalytic degradation of methyl orange (MO) was studied. The catalysts were characterized by scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, selected area electron diffraction, X‐ray photoelectron spectroscopy, and UV‐Vis diffuse reflectance spectroscopy. The results indicate that the 0.1 ZnCo2O4/Ag3PO4 composite system has good photocatalytic activity in the degradation of methyl orange. Under simulated sunlight conditions, the degradation rate can reach 94% after 30 min. The maximum reaction rate constant of 0.1 ZnCo2O4/Ag3PO4 was 0.05301 min−1, which is 3 times and 52 times the rate constant of pure Ag3PO4 and pure ZnCo2O4, respectively. In catalyst recycling experiments, 0.1 ZnCo2O4/Ag3PO4 still degraded methyl orange at a rate of 84.4% after three cycles. Trapping experiments showed that holes and superoxide radicals mostly contributed to the photocatalytic degradation of methyl orange by the catalyst, while hydroxyl radicals played a partial role. The energy level structure of ZnCo2O4/Ag3PO4 is conducive to the effective separation of photogenerated electrons and holes, improving the lifespan of photogenerated charges. In the investigated catalyst series, 0.1 ZnCo2O4/Ag3PO4 demonstrated the best photocatalytic performance.

Quercetin-mediated green synthesis of Au/TiO2 nanocomposites for the photocatalytic degradation of antibiotic ciprofloxacin

Contaminated water is one of the world’s largest health and environmental problem. Emerging pollutants, such as pharmaceutics, are raising increasing concerns, as they are non-regulated toxic chemicals found in low concentrations that are very resilient to conventional water treatments. In the search for effective methods to address this problem, photocatalysis arises as a possible solution to degrade organic pollutants. TiO2 is one of the most widely used catalysts, but the reduced photoactivation under visible radiation constitutes a major drawback. The inclusion of plasmonic nanoparticles, such as gold (AuNPs), can improve the ability to absorb visible radiation from sunlight. AuNPs synthesis methods include toxic and expensive reagents. Herein, an alternative method is proposed, using the flavonoid quercetin to act as the reducing agent in the deposition of AuNPs on the surface of TiO2 (Au/TiO2). The method is optimised, and different loadings of gold are tested. The characterisation of Au/TiO2 confirms increased absorption in the visible wavelength range with increasing concentrations of gold as well as a reduction in the energy band gap. The photocatalytic efficiency of Au/TiO2 was evaluated for the degradation of the antibiotic ciprofloxacin under UV and simulated sunlight irradiation, obtaining a maximum degradation of 86 and 95%, respectively.

Photocatalytic CO2 reduction and destruction of rhodamine B on Bi0/BiOCl with tunable oxygen vacancies induced by 60 CO γ-rays irradiation

In this work, Bi0/OVs-BiOCl photocatalysts were in-situ constructed by irradiating BiOCl with 60Co γ-rays. The powerful penetrating ability of γ-rays induce the Bi-O bonds in BiOCl to break, thereby leading to the deoxygenation (OVs) and the formation of metal Bi0. The presence of Bi0 and OVs endows the photocatalysts with enhanced separation of photogenerated charges and enriched active sites. Under the excitation of simulated sunlight, the BOC-5 sample with an irradiation dosage of 5 KGy demonstrates the best photocatalytic performance, and the yield of CO on the sample is 2.19 μmol·g−1·h−1, which is 2.27 times higher than that on the reference sample. In-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) reveals the formation of intermediates during the conversion of CO2 to CO. Under irradiation of a 300 W xenon lamp, the degradation rate of rhodamine B (RhB) on the BOC-5 sample is 0.05843 min−1, which is 3.42 times of that on the reference sample (0.01708 min−1). The main active species in the degradation process were explored using electron paramagnetic resonance (EPR) and free radical capture experiments at room temperature. This study provides a novel strategy for the preparation of BiOCl-based photocatalysts with high photocatalytic activity through 60Co γ-rays irradiation.

A novel all-solid-state Z-scheme BiVO4/Ag/Cu2O heterojunction: Photocatalytic and photothermal synergistic catalysis of tetracycline under simulated sunlight irradiation

The possible hazards posed by tetracycline (TC) to the environment and public health have made it a critical concern. In this work, the all-solid-state Z-scheme heterojunction BiVO4/Ag/Cu2O nanocomposites (NCs) were synthesized through a hydrothermal approach for the purpose of achieving efficient degradation towards TC. BiVO4/Ag/Cu2O NCs were able to efficiently degrade TC when exposed to simulated sunlight. The results showed that the photocatalytic efficiency was significantly influenced by Cu2O and Ag nanocrystals. The presence of Ag with large light absorption capability facilitated the efficient electron (e-) transfer between BiVO4 and Cu2O nanocrystals, thereby expanding the spectral range of light absorption in BiVO4/Cu2O NCs. Under photocatalytic and photothermal synergistic conditions, BiVO4/Ag/Cu2O NCs with an optimal addition of Ag were able to degrade TC within 60 min at reaction rate constant (k) of 0.04816 min−1. It was discovered that the best-performing photocatalysts (BAC-2) achieved photothermal conversion rates as high as 27.9 %, and they could exhibit outstanding photocatalytic and photothermal efficiency even after six cycles. Furthermore, the results obtained in radical trapping experiments suggested that photogenerated holes (h+), electrons (e-), superoxide radicals (·O2-), hydroxyl radicals (·OH) and singlet oxygen (1 O2) were involved in the photocatalytic degradation of TC. In the context of practical application, the effects of different initial TC concentrations and different irradiation conditions were studied in depth. In addition, the all-solid-state Z-scheme heterojunction mechanism for degrading TC was put forward. This research endeavors to broaden the application scope of all-solid-state Z-scheme heterojunction photocatalysts, with the aim of achieving significantly improved photocatalytic degradation of antibiotic pollutants.

Construction of g-C3N4@Bi-MOF@BiOCl double Z-type heterojunctions for photodegradation of antibiotics under visible light irradiation: Mechanism, pathway, and toxicity assessment

In this study, flower-like microspheres dispersed double Z-type heterojunction g-C3N4@Bi-MOF@BiOCl photocatalysts were prepared using Bi-MOF as the structural template. The photocatalyst showed good degradation ability for both tetracycline antibiotics under simulated sunlight irradiation, as well as stable recyclability and total organic carbon mineralization (TOC). This excellent photocatalytic activity was mainly attributed to the formation of double Z-type heterojunctions that accelerated charge separation and transfer and drove stronger redox capacity. In addition, the effects of conditions such as catalyst dosage, initial concentration of tetracycline hydrochloride (TC) and initial pH (3–11) value of the solution on the photocatalytic reaction were investigated. The results of free radical trapping experiments and ESR analyses indicated that O2−, h+ and OH were the active free radicals that could not be neglected for the degradation of tetracycline hydrochloride (TC), and a possible degradation mechanism was further proposed. Finally, the possible pathways for degradation of the intermediates were rationally deduced by gas chromatography (GC–MS) and evaluated by ecotoxicity analysis based on the utilization rate (T.E.S.T.) of the intermediates produced. This study provides an effective idea for the rational design and synthesis of highly efficient dual Z-type photocatalysts for antibiotic contamination in water-polluted environments.

Molecular Engineering of Multivariate Porous Aromatic Frameworks for Recovery of Dispersed Uranium Resources

AbstractUranium plays an indispensable role in the sustainable development of nuclear industry, and the recovery of uranium from nuclear wastewater is one way to solve the shortage of uranium resources. However, the recovery of uranium resources from nuclear wastewater remains a challenge due to the interfere of coexisting ions. Herein, ratios of the adsorption group and photocatalytic enrichment group are well‐designed and controllably assembled into the porous aromatic frameworks (PAFs) using molecular engineering strategy to realize high uranium recovery efficiency and high resistance to interfering ions. The optimally coordinated multivariate PAF material PAF‐AN2T8‐AO exhibits bifunctions of adsorption and photocatalytic enrichment and thus, achieves high enrichment selectivity and high uranium recovery efficiency of 99% under simulated sunlight irradiation. Compared to PAFs with only adsorption group or photocatalytic group, the uranium recovery capacity of the optimized PAF is enhanced by 1.2 times and 2.3 times, respectively. Mechanistic studies reveal that the product of photocatalytic uranium on PAF‐AN2T8‐AO is air‐stabilized solid crystal metastudtite ((UO2)O2∙2H2O). This work provides a guiding method for designing adsorption‐photocatalytic bifunctional materials and proposes a more environmentally adaptable strategy for dispersed uranium resource recovery.

CuO/ZnO heterojunction nanofilm for effective photocatalytic disinfection

Pathogenic bacteria can spread rapidly from contaminated surfaces to human skin once humans touch such surfaces, resulting in contact infection and subsequent bacterial infectious diseases. In addition to the bacterial drug resistance induced by overuse of antibiotics, the commonly used antibiotic bacteria-killing strategy is unsuitable for surface sterilization of facilities. Herein, a heterojunction CuO/ZnO nanofilm was constructed on glass plates by calcination and atomic layer deposition. This film exhibited excellent photocatalytic antibacterial activity under visible light. The heterostructure between CuO and ZnO at the interface accelerated the separation of photogenerated electrons and holes, resulting in increased yield of reactive oxygen species, which effectively kill bacteria. After 5 min of simulated sunlight irradiation, the antibacterial efficiencies of CuO/ZnO against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were 99.68 ± 0.31 % and 96.49 ± 0.78 %, respectively. The photocatalytic antimicrobial nanofilm synthesized in this study can potentially be used for rapid and safe disinfection of contact surfaces in public facilities.

Influence of deployment method and maintenance on efficacy of sticky card traps for Halyomorpha halys (Hemiptera: Pentatomidae).

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive pest which feeds on numerous economically significant crops. Many integrated pest management strategies for this species rely on effective season-long monitoring for H. halys populations, including attract-and-kill and threshold-based insecticide sprays. Previous studies have shown that a black pyramid trap effectively captures all mobile life stages of H. halys, however, these bulky, ground-deployed traps can be impractical in active orchard rows. Clear sticky cards have been used as a more practical tool for monitoring when paired with the H. halys aggregation pheromone and synergist. Here, the efficacy of deploying single- or double-sided sticky cards hanging in trees or deployed on wooden stakes was compared to standard black pyramid traps over 2 years. The efficacy of single-sided sticky cards deployed on wooden stakes was also evaluated after occlusion of 25%, 50%, or 75% of the surface area by 2D inert materials and 3D organic matter. Single-sided sticky cards were also exposed to simulated sunlight and rainfall for 0, 4, 8, and 12 wk before deployment on wooden stakes. Captures of H. halys adults using sticky cards deployed on wooden stakes were comparable to pyramid traps. Occlusion of cards by 25% or more of any material type led to a decrease in H. halys captures, however, weathering did not influence capture. These data show that clear sticky cards deployed on wooden stakes are effective for season-long monitoring of H. halys in apple orchards, and card replacement should be driven by maintenance of cleanliness.

Novel N-ZnO/p-BN adsorption-photocatalytic composites with interfacial bonding for efficient synergistic degradation of pollutants in water

Exploring green methods for removing organic pollutants from water bodies has attracted significant attention. In this research, N-ZnO/p-BN adsorption-photocatalytic composites were prepared by a simple solvothermal method, and various analytical characterizations confirmed the formation of B-O-Zn bonds at the heterojunction interface that facilitated the separation of photogenerated carriers and revealed a type-II mechanism of charge transfer in the heterostructure. The photodegradation efficiency for oxytetracycline (OTC) by composites with different N-ZnO loadings was investigated under simulated sunlight, and the degradation efficiency of the optimal sample (50 wt% N-ZnO/p-BN) for 50 mg/L OTC reached 92.2 % at 120 min. Efficient pollutant enrichment, broadened light absorption range, high dispersion of the photocatalysts, and effective charge migration are all important factors for improving photocatalytic activity. Furthermore, the photocatalytic process was further investigated, experiments showed that the N-ZnO/p-BN composites were universally applicable under a variety of conditions and possessed the characteristics of low dosage and high degradable concentration. Finally, a rational photocatalytic mechanism was proposed for the degradation system and the degradation pathways of the main degradation model OTC were analyzed and deduced. Therefore, this study provides new ideas for designing high-performance adsorption-photocatalytic composites.

Improved naphthalene photodegradation rate of CN/Pt-P25 photocatalyst by effectively tuning Pt chemical states via H2 secondary annealing

Photocatalytic technology holds promising prospects for remediating naphthalene pollution in water bodies. In this work, the CN/Pt-P25 photocatalyst was successfully prepared via photodeposition combined with co-pyrolysis methods, and employed for naphthalene photodegradation under simulated sunlight. The chemical state of Pt was found to have a significant impact on the photocatalytic activity. H2 secondary annealing effectively tuned Pt chemical states, increasing the proportion of Pt0 species on the CN/Pt-P25 photocatalyst from 41.91 % to 62.24 %. The improved proportion of Pt0 species proportion led to a reduction in the bandgap, which induced changes in the band positions and notably enhancing the separation efficiency of photogenerated electron-hole pairs. Under simulated sunlight irradiation, (H2) CN/Pt-P25 photocatalyst achieved complete naphthalene photodegradation within 100 min. Thus, photocatalysts containing a high proportion of Pt0 species exhibited an improved performance in naphthalene photodegradation. These findings provide new insights into the application of photocatalytic technology for the remediation of PAHs.

Enhanced photothermal conversion properties of graphene aerogel surface and its application in oil spill treatment

As an environmentally friendly material, graphene aerogel has been widely studied. The photothermal conversion performance is an important property of graphene aerogel. Graphene aerogels were prepared by hydrothermal reduction method. The factors affecting its surface photothermal conversion properties were explored and graphene aerogels with ideal photothermal conversion properties were obtained. In addition, COMSOL Multiphysics simulation was carried out to further analyze the intrinsic factors affecting the photothermal properties of the materials. The prepared materials were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectrometry (Raman) to obtain their physicochemical properties. UV–visible-near infrared spectrophotometer and microcomputer-controlled electronic universal testing machine were used to evaluate the light-absorbing capacity and mechanical properties of the materials. The obtained graphene aerogel can be rapidly heated up to higher than 110 °C in 8 s on its surface under simulated sunlight (1000 W·m−2) irradiation. When used for the treatment of oil spill at sea, the prepared graphene aerogel with good photothermal conversion ability can adsorb 105.61 times of its own weight of crude oil and the adsorption rate is as high as 10.56 g·g−1·min−1, which shows a broad application prospect.

Construction of 0D Ti3C2Tx MXene nanoparticles sensitized 1D TiO2 nanotube arrays for enhanced photocatalytic and photoelectrochemical properties

Developing efficient photocatalysts with highly active facets and appropriate cocatalyst hybridization to form heterostructure is a valid way to expedite the separation of photoexcited electron-hole pairs. Herein, a novel 0D/1D Ti3C2Tx MXene/TiO2 photocatalyst was fabricated for photoelectrochemical (PEC) water splitting and tetracycline antibiotic photocatalytic degradation. Meanwhile, highly-exposed TiO2 nanotube arrays were prepared by electrochemical anodizing method, and Ti3C2Tx nanoparticles with mixed terminal group were uniformly grown on the surface of TiO2 through the hydrothermal and solvothermal process, respectively. Compared with pure TiO2, the Ti3C2Tx/TiO2 heterostructure exhibited different degrees of enhancement in PEC and photocatalytic degradation activities under simulated sunlight. The TNT/M-h sample yielded a photocurrent density of 1.77 mA cm−2 at 0 V (vs. SCE) and achieved a 95.57 % photocatalytic removal rate of tetracycline within 140 min. The excellent performance originated from the strong interfacial contact and work function discrepancy between the ordered tubular structure of TiO2 and 0D Ti3C2Tx nanoparticles, which realized the high-efficiency photogeneration and transfer of electron-hole pairs.

The electrically controlled dimming film of thiol-vinyl ether system with low-voltage and high contrast ratio for smart windows

As a type of smart window, polymer dispersed liquid crystal (PDLC) electrically controlled dimming film can respond to external electrical stimuli to regulate the optical flux of sunlight, reducing energy consumption. Herein, a PDLC film was prepared by systematically studying the functionalities and structural compatibility of vinyl ether and thiol compounds, and the optimal PDLC film possesses a superior contrast ratio (CR) of 196.9. When the film thickness is adjusted to 8 μm, the film saturation voltage is reduced to 6.7 V, still maintaining a high CR of 48.4. The well-designed PDLC films exhibited excellent modulation of light. The temperature difference between PDLC film and bare ITO glass can reach 4 °C under the simulated sunlight test, demonstrating the good thermal insulation performance. This smart films with low power consumption and high CR can meet the demand for active regulation of optical flux on smart windows.

Up-conversion luminescence and Bi SPR effect promoted Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst for efficient photocatalytic hydrogen production with simultaneous degradation of malachite green

Photocatalytic hydrogen production with simultaneous degradation of organic pollutants by using solar energy provide a promising strategy to solve the energy and environmental issue in the future. However, for onefold wide band-gap semiconductor, the poor photocatalytic efficiency limits its application on a large scale due to its easy recombination of photo-generated electron-hole pairs and low solar energy utilization. Herein, a novel Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst is prepared via photo-assisted isoelectric point method. In this composite photocatalyst, up-convention luminescence material, NaYF4:Er,Yb,Tm, can offer more ultraviolet light and visible light to intensify the activations of BiOBr and metal Bi nanoparticles, respectively. Furthermore, the formation of Z-scheme BiVO4(040)-BiOBr photocatalystic sytem, the spatial separation of the BiVO4(040) and BiVO4(110) facets and the presence of metal Bi surface plasmon resonance effect are contributed to the high-efficiency separation of the photo-generated electron-hole pairs. The experimental results show that as-prepared Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst exhibits advanced photocatalytic hydrogen production amount (192.0 μm) and excellent degradation ratio of malachite green (88.51 %) under simulated sunlight irradiation for 5.0 h. The apparent quantum yield of the Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst at 420 nm reaches a specific value of 5.8 %. In addition, Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst also remains a high stability in the photocatalytic hydrogen production with simultaneous degradation of malachite green within six reuse. At last, the possible reaction mechanism and degradation pathways of malachite green caused by Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst under simulated sunlight irradiation are put forward.

Rational design of nitrogen and carbon co-decorated mesoporous TiO2 composites for photocatalytic selective oxidation of alcohols

Photocatalytic organic synthesis has attracted much attention in recent years. Herein, a N and C co-decorated mesoporous TiO2 (mp-NCT) photocatalyst was synthesized for selective oxidation of alcohols. Notably, the as-prepared mp-NCT composites possess large specific surface areas and mesoporous structures, which could provide sufficient active sites and improve mass transfer. Furthermore, the co-doping of N and C species could not only extend the light absorption, but also tune the valence band of TiO2. Meanwhile, numerous oxygen vacancies and intra-band could be introduced, which helps to reduce the combination of the photogenerated carriers. As a result, the mp-NCT composites show excellent photocatalytic performance towards selective oxidation of benzyl alcohol and its derivatives to corresponding aldehydes under simulated sunlight irradiation. Mechanism studies revealed that the photogenerated electrons, holes and high dynamic equilibrium concentration of O2•- radicals were responsible for the efficient conversion of alcohols to aldehydes.

Piezoelectric assisted boosting photocatalytic hydrogen evolution over a finely prepared Pt/TiO2/g-C3N4 composite system using lactic acid as sacrificial agent

A one-step calcination method was employed to fabricate a new TiO2/g-C3N4(TCN) composite catalyst. The therein TiO2 nanoparticles with good dispersion were synthesized through a sol-gel method and followed by additional heat treatment. The ultra-thin and flat g-C3N4(CN) nanosheets were synthesized by calcining a mixture of urea and melamine. The obtained TCN exhibited significantly excellent performance, especially when 3 wt% Pt was added and lactic acid (HL) was used as a sacrificial agent, achieving a rate of 32.5 mmol/h/g. This improvement can be attributed to the uniform dispersion of nano TiO2 particles on g-C3N4, the flat ultra-thin layer structure of CN, and the constructed heterojunctions between two, which promote the separation of photogenerated electron-hole pairs. Measurements of PL and photocurrent response confirmed enhanced efficiency in interface charge separation and transfer. Additionally, it demonstrated lower internal resistance in EIS tests. Notably, owing to the piezoelectric properties of CN, when the reaction liquid was subjected to additional ultrasonic treatment, the hydrogen production rate further increased to 43.57 mmol/h/g and 2.9 mmol/h/g, respectively, in simulated sunlight and visible light response. The piezoelectric effect of CN induced by ultrasound regulated the bandgap width of the catalysts, broadening their response to visible light.

Exploring photocatalytic tetracycline removal performance under simulated sunlight irradiation: Milling time effect on metallic reduction of MnO/ZrO2 mixed oxide

In the present research, it is reported that ball milling technique can be applied to enhance the photocatalytic properties of MnO and ZrO2 metal oxide powders (MZOx) furthermore the fabricated photocatalyst can be used for the degradation of tetracycline (TTC). XRD analyses revealed that increasing the milling time resulted in the formation of a pure metallic Mn crystal phase, which boosted the antibiotic degradation rate. It was confirmed by SEM technique that the morphological structures of the particles were generally small and uniform. The band gap energy was calculated as 3.70 eV for the hybrid metal oxide. Additionally, the adsorptive and photoluminescence features were illuminated via DRS and PL analyses. The effect of milling time had a major impact on the photodegradation rate of TTC, and the 8 h milling sample (MZOx-8h) exhibited the highest catalytic degradation activity (79.4 %). Low photocatalytic activity was obtained at acidic pHs and increased at alkaline pHs. The presence of H2O2 sharply decreased photocatalytic process time (60 min) and 94.3 % of the TTC was degraded at 7.5 mM H2O2. The photocatalytic degradation process proceeded through superoxide radicals and was supported by holes. The stability of MZOx-8h almost remained constant (70.02 %) even after seven cycles. It was determined that the presence of oxalic acid positively affected the progress of TTC degradation reactions. Further, practical application areas were investigated and MZOx-8h doped on support materials was found to be suitable for such applications in proportion to the doping ratio. Finally, it was demonstrated that MZOx-8h exhibited remarkable performance in photocatalytic reactions of different types of organic pollutants. The synergistic nature of MnO and ZrO2 with the contribution of ball milling time effect resulted in high photocatalytic activity.

Hydrothermal synthesis and characterization of 0D/2D SrMoO4/g-C3N4 composite with direct Z-scheme heterojunction: Efficient photocatalytic Ciprofloxacin degradation

Ciprofloxacin (Cip) is a common pollutant that causes sewage problems, and its effective removal is a great contribution to the clean water environment. Direct Zener-scheme (Z-scheme) heterojunction photocatalyst is a promising design idea for the removal of residual antibiotics in water. The goal of this study is to construct a binary composite photocatalyst with Z-scheme heterojunction to effectively remove residual ciprofloxacin in wastewater. Herein, a direct Z-scheme 0D/2D SrMoO4/g-C3N4 (SMOCN) composite photocatalyst was synthesized by ultrasonic-assisted hydrothermal way and its interior information (chemical structure, micromorphology, and physic-optical property) was detected by various characterization instruments (XRD, FT-IR, EDX, XPS, UV–Vis DRS, and PL). Meanwhile, the photocatalytic activity of all-prepared catalysts were estimated by Cip photodegradation experiments under simulated sunlight (500 W Xenon lamp). Among them, 89.9 % of Cip was broken down by 30SMOCN composite within 180 min at pH 7.0, which respectively reached 2.56 times of bare SMO and 2.03 times of bare CN. Furthermore, 85.2 % of Cip targeted molecule is still removed by SMOCN (excellent stability and recyclability) after five cycle runs. Finally, the reasonableness of SMOCN conforming to the direct Z-scheme mechanism is verified by comparison of optical properties, quenching experiment results and photogenerated carrier migration paths: 1) There is optical complementarity between SMO and CN, which is represented by redshifted absorption edge, narrowed band gap and weaken PL intensity. 2) The key active site on the SMOCN composite surface is photogenerated carriers in Cip photocatalytic degradation, which given full play to the direct synergistic catalytic effect between SMO and CN heterojunction. 3) The direct Z-scheme mechanism preserves the carriers of SMOCN with effective photo-redox function, promotes their separation and prolongs their lifetime.

Photocatalytic persulfate activation by silica microsphere-supported g-C3N4 for efficient carbamazepine degradation

A silica-loaded g-C3N4 composite photocatalyst (M-SiO2/g-C3N4) was prepared by grinding amorphous SiO2 microspheres (M − SiO2) with melamine and calcining the resulting grinding products. This composite was used for photocatalytic persulfate (PMS) activation to degrade carbamazepine (CBZ). The results showed that the degradation efficiencies of CBZ by M-SiO2/g-C3N4-2.5 (39.16 % of g-C3N4)-activated PMS were 78.92 % and 100 % after simulated sunlight irradiation for 60 and 120 min, respectively. These values were significantly greater than those of the system with pure g-C3N4 (29.15 % and 42.4 %). In particular, the degradation efficiency of CBZ with M-SiO2/g-C3N4-2.5 decreased by only 9.47 % after 4 cycles of recycling. In the catalytic process, h+, SO4•− and O2•− were the main reactive species contributing to CBZ degradation. Compared with g-C3N4, loading g-C3N4 on the surface of M − SiO2 resulted in a decrease in g-C3N4 lamellar stacking, which increased the number of active surface sites and improved the separation and migration of photogenerated carriers, improving the degradation performance.

Insight into the photodegradation of methylisothiazolinone and benzoisothiazolinone in aquatic environments

Methylisothiazolinone (MIT) and Benzisothiazolinone (BIT) are two widely used non-oxidizing biocides of isothiazolinones. Their production and usage volume have sharply increased since the pandemic of COVID-19, inevitably leading to more release into water environment. However, their photochemical behaviors in water environment are still unclear. Therefore, this study investigated photodegradation properties of MIT and BIT in natural water under simulated sunlight. The results demonstrated that direct photolysis was mainly responsible for their photodegradation which occurred through their excited singlet states rather than triplet states. The quantum yields of MIT and BIT photodegradation were 11 - 13.6 × 10−4 and 2.43 - 5.79 × 10−4, respectively. pH had almost no effect on the photodegradation of MIT, while the photodegradation of BIT was significantly promoted under alkaline condition due to abundance of BIT in its deprotonated form (BIT-N−). Cl−, NO3− and dissolved organic matter (DOM) in natural water inhibited the photodegradation of both MIT and BIT, with the light screening effect of DOM being the most significantly inhibitory factor. The addition of other isothiazolinones, which possibly coexisted with MIT and BIT in actual condition, slightly inhibited the photodegradation of MIT and BIT. The estimated half-life under natural sunlight at a 30°N latitude was estimated to be approximately 1.1 days. The photodegradation pathways of MIT and BIT are similar, primarily initiated from the ring-opening at the N-S bond, with Frontier electron densities (FED) calculations suggesting the likelihood of oxidation and ·OH addition reactions at the O, N, and S sites. While the photodegradation products exhibited significantly reduced acute toxicity compared to their parent compounds, they nonetheless posed substantial chronic toxicity. These insights are vital for assessing the ecological impacts of MIT and BIT in aquatic environments.