Visible Light Responsive Photocatalysis Research Articles

Role of self-assembly coated Er3+: YAlO3/TiO2 in intimate coupling of visible-light-responsive photocatalysis and biodegradation reactions

Conventionally used ultraviolet light can result in dissolved organic carbon (DOC) increasing and biofilm damage in intimate coupling of photocatalysis and biodegradation (ICPB). Visible-light-responsive photocatalysis offers an alternative for achieving ICPB. In this study, composite-cubes were developed using self-assembly to coat a thin and even layer of visible-light-responsive photocatalyst (Er3+: YAlO3/TiO2) on sponge-type carriers, followed by biofilm cultivation. The degradations of phenol (50mgL−1) were compared for four protocols in circulating beds: adsorption (AD), visible-light-responsive photocatalysis (VPC), biodegradation (B), and intimately coupled visible-light-responsive photocatalysis and biodegradation (VPCB). The phenol and DOC removal efficiencies using VPCB in 16h were 99.8% and 65.2%, respectively, i.e., higher than those achieved using VPC (71.6% and 50.0%) or B (99.4% and 58.2%). The phenol removal of 96.3% could be obtained even after 3 additional cycles. The 6.17-min intermediate detected by HPLC, continuously accumulated for VPC, appeared at 1–6h and then was completely removed for VPCB in 10h. ICPB was further illustrated in that most of the biofilm was protected in the carrier interiors, with less protection on the carrier exterior in VPCB. A self-regulation mechanism that helped photocatalyst exposure to visible-light irradiation was identified, promoting the combined photocatalysis and biodegradation.

Synergistic photocatalytic properties and mechanism of g-C3N4 coupled with zinc phthalocyanine catalyst under visible light irradiation

Visible light-responsive photocatalysis has shown great potential for effluent treatment as an environmentally friendly method. Herein, the photocatalyst of graphitic carbon nitride (g-C3N4) coupled with zinc phthalocyanine (g-C3N4/ZnTcPc) was prepared by immobilizing zinc tetracarboxyphthalocyanine (ZnTcPc) onto g-C3N4 covalently. The spectral response region of g-C3N4 has been extended from 450nm to more than 800nm sensitized by ZnTcPc, which is well known for the red/near-IR (Q band) light absorption. Compared with pure g-C3N4 and ZnTcPc, g-C3N4/ZnTcPc presented a significantly enhanced photocatalytic activity for the degradation of rhodamine B (RhB) and 4-chlorophenol (4-CP) under visible irradiation. The photocatalytic activity of g-C3N4 has been improved by the coupled interaction with ZnTcPc over a wide pH range. Moreover, besides photogenerated hole, the presence of singlet oxygen (1O2), superoxide radical (O2−) and hydroxyl radical (OH) has been evidenced in the visible light-responsive catalytic system with g-C3N4/ZnTcPc, especially in alkaline condition. The possible photocatalytic degradation pathway of RhB has been proposed according to the results of ultra-performance liquid chromatography and high-definition mass spectrometry (UPLC Synapt G2-S HDMS). This synergistic photocatalytic process will provide useful insights to make full use of solar light for future application to eliminate recalcitrant organic pollutants.

Cost-effective and eco-friendly synthesis of novel and stable N-doped ZnO/g-C3N4 core–shell nanoplates with excellent visible-light responsive photocatalysis

N-doped ZnO/g-C3N4 hybrid core-shell nanoplates have been successfully prepared via a facile, cost-effective and eco-friendly ultrasonic dispersion method for the first time. HRTEM studies confirm the formation of the N-doped ZnO/g-C3N4 hybrid core-shell nanoplates with an average diameter of 50 nm and the g-C3N4 shell thickness can be tuned by varying the content of loaded g-C3N4. The direct contact of the N-doped ZnO surface and g-C3N4 shell without any adhesive interlayer introduced a new carbon energy level in the N-doped ZnO band gap and thereby effectively lowered the band gap energy. Consequently, the as-prepared hybrid core-shell nanoplates showed a greatly enhanced visible-light photocatalysis for the degradation of Rhodamine B compare to that of pure N-doped ZnO surface and g-C3N4. Based on the experimental results, a proposed mechanism for the N-doped ZnO/g-C3N4 photocatalyst was discussed. Interestingly, the hybrid core-shell nanoplates possess high photostability. The improved photocatalytic performance is due to a synergistic effect at the interface of the N-doped ZnO and g-C3N4 including large surface-exposure area, energy band structure and enhanced charge-separation properties. Significantly, the enhanced performance also demonstrates the importance of evaluating new core-shell composite photocatalysts with g-C3N4 as shell material.

Immobilized Cu–Cr layered double hydroxide films with visible-light responsive photocatalysis for organic pollutants

Oriented Cu–Cr layered double hydroxide (LDH) films have been fabricated by the electrophoretic deposition method (EPD) on copper substrates, which can be used as photocatalysts for the degradation of organic pollutants under visible-light irradiation. Powder X-ray diffraction (PXRD), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and Brunauer–Emmett–Teller (BET) reveal that the resulting CuCr-LDH film possesses high crystallinity, porous structure as well as large specific surface area. UV–vis diffuse reflection spectroscopy (DRS) confirms that the CuCr-LDH film shows a broad absorption in visible light region (>400nm). The LDH film thickness can be controlled precisely by adjusting voltage or time of EPD. The film with thickness of 16.5μm shows excellent photocatalytic activity for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP), sulforhodamine B (SRB) and Congo red. The photocatalytic reaction kinetics of 2,4,6-TCP was appropriately described by the pseudo-first-order model. In addition, the LDH film exhibits excellent recycleability compared with the corresponding powder sample, which facilitates its repeatable and cyclic usage over a long period. Owing to the high efficiency, low-cost preparation, easy manipulation and recyclability, it is expected that this film can be potentially used as photocatalyst in the field of water treatment.