Visible-light Photocatalytic System Research Articles

Enhanced Visible Light Photocatalytic Activity of Exfoliated Boron‐TiO2 Composite for Degradation of Rhodamine B and Nitrogen Fixation

AbstractThe design of an efficient, recyclable, visible light photocatalytic system was examined as a viable new green way to address environmental challenges such as removal of pollutants from wastewater and N2 fixation. The exfoliated boron (Bexf)‐Titanium oxide (TiO2) composite visible light active photocatalysts were successfully constructed via a simple wet chemical method by utilizing acetone as a solvent. The composite was evaluated for the photodegradation of Rhodamine B (RhB) dye and reduction of N2, which exhibits improved photocatalytic activity for degradation of RhB as well as for reduction of N2. Experiments with different quenchers indicate that the photogenerated superoxide radical anion (O2⋅−) plays a significant role in the degradation of RhB as well as for N2 reduction reactions. The composite catalyst shows good photostability and there is no significant reduction of the catalyst activity for dye degradation up to 4 cycles of reaction. This work affords a significant view into the design of reusable TiO2 composite materials for photocatalytic RhB degradation and nitrogen fixation.

Degradation of Dye Wastewater by a Novel mBT-MPR Visible Light Photocatalytic System

The high efficiency and low consumption green wastewater treatment technology has important practical significance for the recycling of printing and dyeing wastewater. The efficiency of visible light catalytic degradation of organics is greatly affected by the performance of the catalyst and the photo reactor. Therefore, Bi2WO6/TiO2/Fe3O4 (mBT) visible light photocatalyst was accurately prepared by the ammonia iron double drop method. In order to improve the photodegradation efficiency, a tubular magnetic field-controlled photocatalytic reactor (MPR) was developed. The novel mBT-MPR visible light photocatalytic system was proposed to treat RhB simulated wastewater. The experimental results showed that when the dosage of mBT catalyst was 1 g/L and visible light was irradiated for 60 min, the average removal rate of rhodamine B (RhB) with initial an concentration of 10 mg/L in the simulated wastewater for four times was 91.7%. The mBT-MPR visible light photocatalysis system is a green and efficient treatment technology for organic pollutants in water with simple operation, low energy consumption, and no need for catalyst separation.

Visible light-driven chlorite activation process for enhanced sulfamethoxazole antibiotics degradation, antimicrobial resistance reduction and biotoxicity elimination

In this study, a visible light-driven chlorite activation process, i.e., the combined ClO2-photocatalysis process, was constructed to efficiently produce chlorine dioxide for the enhanced degradation of the sulfamethoxazole antibiotic from aqueous solutions. The superiority of the combined ClO2-photocatalysis process compared to visible light photocatalytic system, and chlorine dioxide oxidation process was systematically investigated. The addition of chlorite in the BiOI-based visible light photocatalytic system achieved 100% removal of sulfamethoxazole within 30 min, surpassing both the photocatalytic system (16%) and chlorine dioxide oxidation process (70%). The degradation constant rate (k) was 0.0771 min−1, which was 2.7 times and 51.4 times higher than the chlorine dioxide oxidation process and photocatalytic system, respectively. Water matrix conditions including pH, inorganic ions, and organic matter had little effect on the degradation efficiency of sulfamethoxazole in the combined ClO2-photocatalysis process. Moreover, antibiotic-resistant bacteria can be effectively inactivated and the production of toxic chlorine-containing intermediates and disinfection byproducts is significantly inhibited. This combined ClO2-photocatalysis process takes advantage of photogenerated radicals to activate chlorite to chlorine dioxide, which not only promotes electron-hole separation, but also exhibits high efficiency, durability, resistance to external environment disturbances, and environmental safety, making it a good candidate for the efficient, green, and sustainable treatment of pharmaceutical wastewater.

Effective BiOCl Electrons Collector for Enhancing Photocarrier Separation of Bi2WO6/BiOCl Composite

Enhancing photocarrier separation is a key step of photocatalysis, and in situ constructed composition interface is an advanced method to achieve this aim. Therefore, we report a face-to-face Bi2WO6/BiOCl (BWOC) which was synthesized via the continuous in situ ion-exchange method. As UV light is harmful to the human body, BWOC exhibits excellent photocatalytic activity only in visible light, and this is an important feature because visible light is a human-friendly operating condition. Under 50 W visible LED lamp illumination, unexcited BiOCl (BOC) only extracts electrons of excited Bi2WO6 (BWO), and holes remain on BWO, resulting in excellent photocarrier spatial separation efficiency through the face-to-face interface. This is why BWOC can be safe to use for the removal of hazardous substances. Compared with BWO and BOC, BWOC possesses 2.6 and 5.6 times higher photodegradation activity than RhB. This work provides a novel insight of efficient visible light photocatalytic system for environmental remediation.

Superoxide generated by blue light photocatalysis of g-C3N4/TiO2 for selective conversion of amines

Reactive oxygen species (ROS) are remarkably reactive chemical oxygen-containing molecules that not only occupy critical positions in cell signaling and homeostasis for regulating aerobic living organism's growth and development but also broadly participate in the environmental management as extraordinary oxidizing agents. Inspired by the behaviors of ROS, we designed an artful visible light photocatalytic system for the selective conversion of amines due to the activation of oxygen (O2) to superoxide (O2–) over g-C3N4/TiO2. Here, blue light was manipulated as a light source to circumvent the initiation of the strong nonselective hydroxyl radical (OH) that is often generated by valence band holes (hvb+) of TiO2. Aerial O2 was employed to achieve the long-lived, exclusive ROS, O2–, while acetonitrile, an aprotic solvent, was utilized to prolong the lifetime of O2–. Importantly, the g-C3N4/TiO2 possesses an exceptional capability for the generation of O2–. Based on the synergistic effect of two ingredients of the g-C3N4/TiO2 photocatalyst, the highly selective conversion of amines was achieved with superior conversions in comparison with the pristine TiO2 and g-C3N4. Furthermore, a mechanism dominated by O2– was proposed according to the kinetic studies, electron paramagnetic resonance (EPR), and ROS quenching experiments. This work highlights the importance of ROS in defining the desirable outcomes over semiconductor photocatalysts.

Chlorine dioxide radicals triggered by chlorite under visible-light irradiation for enhanced degradation and detoxification of norfloxacin antibiotic: Radical mechanism and toxicity evaluation

A novel combined chlorine dioxide (ClO2)-photocatalysis technique was developed by dosing chlorite (ClO2−) in a visible light photocatalytic system. Active ClO2 radicals were produced through the activation of ClO2− by photoinduced ·OH radicals. It is for this reason that the degradation rate of norfloxacin (NOR) in the combined ClO2-photocatalysis system was promoted to 0.2672 min−1, approximately 6.6 times faster than the single photocatalytic system. The durable active ClO2 guaranteed the stability of the combined ClO2-photocatalysis system when facing external interferences, such as pH change, inorganic ions, and natural organic matter (NOM). Quantitative structure–activity relationship (QSAR) prediction and toxicity verification identified effective elimination of biological toxicity of NOR with the assistance of ClO2. Moreover, the residual ClO2− can be retransformed into ClO2 based on the ClO2−/ClO2 dynamic interchange mechanism, facilitating ClO2− residue elimination. ClO2− also served as the sacrificial agent of ·OH for promoting electron-hole separation and protecting photocatalysts from photo-erosion, which was responsible for the outstanding stability in multiple cycle tests. Results showed the novel combined technique can respond well to natural sunlight. This work provides a strategy for designing advanced oxidation processes (AOPs) by integrating ClO2 oxidation and photocatalytic oxidation to achieve degradation and detoxification of antibiotic wastewater under natural sunlight.

Novel stable enhanced visible light photocatalytic system based on a Ag3PO4@polypyrrole core-shell Z-scheme with in-situ generated metallic Ag ohmic contacts

Maintaining the high photocatalytic activity and stability of Ag3PO4 in practical applications is a still a major challenge. In this study, a series of Ag3PO4@polypyrrole (PPy) core-shell structure photocatalysts were prepared successfully by facile in-situ oxidative polymerization. A transmission electron microscopy image of the composite showed that the PPy shell with a thickness of 5–10 nm was coated tightly on the surface of the Ag3PO4 particle core. X-ray diffractometer and X-ray photoelectron spectroscopy analyses demonstrated that the silver ions were reduced to metallic Ag during polymerization. Ultraviolet–visible diffuse reflectance spectra indicated that the light response range of PA-5 broadened from 300 to 630 nm. Compared with pure Ag3PO4, the composites exhibited higher photocatalytic activities and better photostability, especially Ag3PO4@PPy with a PPy content of 5 wt% (PA-5). The degradation rate of PA-5 with organic dyes exceeded 98% within 15 min under visible light irradiation. Even after five repeated reactions, PA-5 still maintained a high degradation rate of 94.98%. The degradation rate of the pure Ag3PO4 decreased significantly from 94.53% to 60.33% after five cycles. Based on the experimental results, a reasonable mechanism is proposed for the Z-scheme electron-transfer photocatalytic system with metallic Ag as an ohmic contact.

Hydrothermal synthesis of an artificial Z-scheme visible light photocatalytic system using reduced graphene oxide as the electron mediator

The electron mediator plays an important role in charge transfer in an artificial all-solid-state Z-scheme system. According to the energy band theory, a visible light photocatalytic system was designed by using reduced graphene oxide (RGO) as the electron mediator. The as-prepared g-C3N4/RGO/Bi2MoO6 composite was synthesized by hydrothermal process, and it was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen sorption, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectrometer (XPS) and diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the g-C3N4/RGO/Bi2MoO6 composite was evaluated by analyzing the degradation of Rhodamine B (Rh B) under visible light irradiation. The photocatalytic degradation rate of Rh B for the g-C3N4/RGO/Bi2MoO6 composite was 8.73 and 5.19 times for the Bi2MoO6 and g-C3N4/Bi2MoO6 composite, respectively. The matched Fermi level structure provided the favorable interfacial charge transfer from the Bi2MoO6 Photosystem II (PS II) to the g-C3N4 Photosystem I (PS I) to promote the photocatalytic degradation of Rh B, suggesting that RGO was a suitable electron mediator in the Z-scheme system. The present study can provide a scientific basis for the rational design and realization of the Z-scheme system in environmental application.

Visible Light Photocatalytic Hydrogen Evolution from Water Reduction Using Eosin y Containing Trace Vitamin B<sub>12</sub> as a Light Harvesting Unit

A visible light photocatalytic system consisting of Eosin Y containing trace vitamin B12 (VB12) as a light harvesting unit, multiwalled carbon nanotubes (MWCNTs) as an electron transfer channel and CuO as a hydrogen evolution center (abbreviated to Eosin Y/VB12-MWCNTs-CuO) was prepared on the basis of the synergistic effect between Eosin Y and VB12 under visible light irradiation. The Eosin Y/VB12-MWCNTs-CuO system exhibits a higher photocatalytic activity of hydrogen evolution than the Eosin Y-MWCNTs-CuO system. The improvement of the photocatalytic activity is probably due to the effective transfer of photogenerated electrons and stabilization of VB12 to excited Eosin Y.

Photostable Self-Cleaning Cotton by a Copper(II) Porphyrin/TiO2 Visible-Light Photocatalytic System

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV-vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications.

Visible light decomposition of ammonia to dinitrogen by a new visible light photocatalytic system composed of sensitizer (Ru(bpy)32+), electron mediator (methylviologen) and electron acceptor (dioxygen)

Visible light decomposition of aqueous ammonia to dinitrogen was successfully achieved by using a new photocatalytic system based on a molecular photoelectron relay composed of a sensitizer (Ru(bpy)(3)2+), an electron mediator (methylviologen) and an electron acceptor (dioxygen), which can be used as a visible light-driven photocatalyst instead of UV-driven semiconductors.