Degradation Efficiency Of Photocatalyst Research Articles

Novel through-holes g-C3N4/BiOBr S-scheme heterojunction: Charge relocation mechanism and DFT insights

A novel multiscale through-holes g-C3N4/BiOBr S-scheme heterojunction with homogeneous morphology was fabricated via a solvothermal method. Notably, the prepared through-holes g-C3N4 yielded a subband gap (2.11 eV) attributed to the fracture and reorganization of triazine ring units, leading to a narrow band gap complex. Photocatalyst A-2 (2.73 eV) was significantly broadened at the absorption edge. A reasonable S-scheme heterojunction charge relocation mechanism was demonstrated based on active species trapping experiments, atomic force microscope (AFM) equipped with a Kelvin probe force microscope (KPFM), and density functional theoretical (DFT) theoretical calculations. The S-scheme g-C3N4/BiOBr heterojunction and the constructed internal electric field facilitate the retention of high redox properties and facilitated charge relocation. Hence, the synergistic interaction between the S-scheme heterojunction and through-holes structure enabled specimens to be exhibited high-efficiency degradation activity. The degradation efficiency of photocatalyst A-2 for TC·HCL and RhB was 94.5% (60 min) and 99.9% (30 min), respectively. At pH = 5.1, the TC·HCL photoreaction time was reduced to 30 min, whereas at pH = 2.3, the RhB photoreaction time was shortened to 15 min. Five repeatable recovery tests still maintain excellent stability. This work contributes new insights into the charge relocation mechanism of S-scheme heterojunction high-efficiency photocatalysts.

Microwave method synthesis and photocatalytic activity of Nano-BiOBr photocatalyst

Nano-BiOBr photocatalysts were successfully prepared by Microwave method using ethylene glycol solution. The nano-BiOBr photocatalysts were characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and the degradation ability of nano-BiOBr photocatalyst to adsorb rhodamine B (RhB) was also explored. The results show that the crystallinity of the nano-BiOBr photocatalyst increases with the increase of the concentration, and increases with increasing growth temperature. Nano-BiOBr microspheres of about two µm were polymerized by different self-assembly methods from nanosheets having a thickness of 10 nm to 15 nm. The concentration and growth temperature have an essential influence on the band gap of the nano-BiOBr photocatalyst. The degradation efficiency of photocatalyst decreases with the increase of concentration, increased with the increase in growth temperature. (e) photocatalyst showed the highest photocatalytic activity for RhB.

Advances in Nanomaterial‐based Water Treatment Approaches for Photocatalytic Degradation of Water Pollutants

AbstractDemand of pure drinking water is increasing day by day in line with both a growing population and global industrialization. Studies in the past few decades on the application of advanced oxidation processes (AOP) for the treatment of wastewater containing perilous organic pollutants, are promising when compared to conventional water treatment methods. In case of AOP, generation of powerful oxidant radicals (.OH, HOO.) is crucial for the purpose of degradation. Several processes for the in‐situ generation of such highly reactive oxidants have been discussed. This Review highlights the literature reports on the degradation of various organic pollutants (dyes, pharmaceuticals, pesticides, herbicides, insecticides) by means of photocatalysis. A number of scientific investigations have been performed, which elucidate suitable properties (band gap energy, carrier transport, crystallinity etc.) for the deliberate design of efficient photocatalysts. The oxidation rates and degradation efficiency of photocatalysts are governed by some basic parameters, like organic pollutant concentration, photocatalyst concentration, pH, reaction temperature, light intensity, irradiation time, inorganic ions, oxidants, and these are also discussed. Titania and titania based materials have many attractive properties (nontoxicity, less costly, advanced optical properties, high stability) towards photo degradation process. Several studies have been reported investigating the intermediates produced during degradation process as well as the final degraded product, which might be toxic and/or hazardous to the human as well as to the environment. This review assimilates elaborate study on the mechanism of photocatalytic degradation of various organic pollutants.

Photocatalytic degradation of azo and anthraquinone dye using TiO2/MgO nanocomposite immobilized chitosan hydrogels

ABSTRACT Textile dyes are very toxic to human beings and environment. TiO2 nanoparticles have been of great interest in treating the organic effluent dyes. While using TiO2 nanoparticles, there is the electron-hole recombination, which decreases the degradation efficiency of photocatalyst. MgO nanoparticle, when used along with TiO2, forming TiO2/MgO nanocomposite act as a barrier for electron-hole recombination. Here, TiO2/MgO nanocomposites have been immobilized in chitosan beads, where chitosan acts as a support for the nanocomposite. The photocatalysts have been characterized by scanning electron microscope, ultraviolet (UV), X-ray diffraction and Fourier transform infrared spectroscopy. Methyl orange (MO) and Alizarin Red S (ARS) were used as model dye compounds. For MO, the experimental data have a better fit with Langmuir adsorption model and for ARS, it has a better fit with Freundlich adsorption model. Photocatalytic degradation efficiency of TiO2/MgO nanocomposite for a reaction time of 90 min towards degrading MO is 83.2% and ARS is 43.8%. Degradation efficiency of TiO2/MgO/chitosan hydrogels towards degrading MO and ARS is 82.4% and 41.8%, respectively. 3 wt.% is found to be the optimum concentration of MgO in TiO2/MgO nanocomposite . Degradation of the dye follows first-order kinetics and Langmuir–Hinshelwood model well suites in describing the kinetics of photocatalytic disappearance of the dyes. First-order rate constants for dye degradation under UV irradiation were calculated. TiO2/MgO/chitosan hydrogels could efficiently degrade MO and ARS dyes with a little lesser efficiency than TiO2/MgO nanocomposite making the process economically and environmentally a very suitable and favourable process for textile dye degradation.

Construction of Ag SPR-promoted step-scheme porous g-C3N4/Ag3VO4 heterojunction for improving photocatalytic activity

In recent years, many effective photocatalysts have been developed in order to solve the problems of organic pollutants. In this work, two–dimensional (2D) porous graphitic carbon nitride/Ag 3 VO 4 (Pg-C 3 N 4 /Ag 3 VO 4 ) composites containing Ag nanoparticles (NPs) have been successfully synthesized by chemical deposition methods. And methylene blue (MB) was used as a model organic pollutants. The MB degradation efficiency of photocatalysts was tested under visible light, and it was found that 40%Pg-C 3 N 4 /Ag 3 VO 4 exhibited the best photocatalytic performance. The MB degradation rate of 40%Pg-C 3 N 4 /Ag 3 VO 4 is 99.3% within 8 min. The improvement of photocatalytic performance of Pg-C 3 N 4 /Ag 3 VO 4 composites was due to the formation of step-scheme heterojunction between Ag 3 VO 4 and Pg-C 3 N 4 . In addition, the porous structure of Pg-C 3 N 4 and Ag surface plasmon resonance (SPR) effect accelerate the separation and transmission of electron-hole pairs, and reduce the probability of recombination. In addition, Ag SPR effect can enhance the absorption of visible light. Moreover, it is found that the superoxide ions ( O 2 − ) and holes (h + ) play a major role in photocatalytic degradation through capture tests. Finally, the possible charge transfer mechanism is proposed. • 2D/2D Pg-C 3 N 4 /Ag 3 VO 4 composite was successfully prepared. • The composite showed high visible light photocatalytic activity. • The composite showed excellent photostability. • Step-scheme photocatalytic mechanism is proposed.

Effects of common metal cations on Ag3PO4-photocatalytic water decontamination

Metal cations existing invariably in natural and waste waters play crucial roles on the degradation efficiency of photocatalysts. Herein, the photocatalytic degradation of methylene blue (MB) on Ag3PO4 in the presence of metal cations (Na+, K+, Mg2+, Ca2+, Zn2+, Mn2+, Cu2+, and Fe3+) was investigated. It was found that the adsorption and the degradation rate of MB on Ag3PO4 are very sensitive to the interfering cations except Na+ and K+. In general, the adsorption and the degradation rate of MB could be strongly inhibited by Zn2+, Mn2+, and Cu2+ even at a low concentration of 0.1mmolL−1, while Mg2+ and Ca2+ show slight suppressing effects. Fe3+ exhibits a unique effect, that is, under low concentration of 0.02–0.1mmolL−1, Fe3+ demonstrates slight enhancement on the adsorption and the degradation of MB, whereas Fe3+ with high concentration of >0.1mmolL−1 causes detrimental effect. Inductively coupled plasma-atomic emission spectrometer and transmission electron microscopy results suggest that the strong adsorption and ionic-exchange of metal cations are the main factors to the inhibited performance of Ag3PO4. The work presents great importance on the practical application of Ag3PO4 for photocatalytic water decontamination; namely, the waters should be pretreated to remove such cations before photocatalytic decontamination.

An Innovative Measurement for Testing the Nanocatalyst Degradation Efficiency of NH3

This study develops a low-cost, fast and innovative measurement method for testing the efficiency of photocatalysts in the degradation of gaseous concentrations. In the past, photocatalyst tests of catalyst response to gases mainly relied on measurement with either GC/MS (Gas Chromatography/Mass Spectrometer) or FTIR (Fourier Transform Infrared Spectroscopy), to monitor the reaction process. However, these two instruments are very expensive, and the processes are complicated and time-consuming. The major devices of the measurement method developed by this study are UV/VIS spectrophotometer and quartz cuvettes. The experimental procedures are not only simple but fast. In the experiment, a gas of a specific concentration is first injected into an enclosed quartz cuvette. The cuvette is then placed in the UV/VIS spectrophotometer to carry out tests to obtain an absorption spectrum. Thus, a calibration curve of UV light absorbance intensity vs. various gaseous concentrations can also be obtained using the same method. The degradation efficiency of the different photocatalysts is to be measured. Quartz plates are coated with two different types of TiO2 nanocatalysts. The coated plates are then placed in separate cuvettes. After injecting NH3 into a quartz cuvette, the cuvette is then put under the UV light irradiation to perform the degradation experiment. Afterwards, the cuvette is transferred to the UV/VIS spectrophotometer for testing. The absorbance intensity of the absorption spectra is then compared with the calibration curves. Based on the change of the gaseous concentration, the degradation efficiency of the photocatalyst is determined. The experimental results reveal that the self-made TiO2 nanocatalyst has excellent degradation efficiency towards NH3. When NH3 is exposed to UV irradiation for 60 minutes, the gaseous concentration can be reduced to 10.35% of the original concentration. However, the commercial TiO2 nanocatalyst can only reduce the gaseous concentration to 50.2% of the original concentration. In addition, the degradation reaction rate constant of the self-made TiO2 nanocatalyst towards NH3 is as high as 0.029 min−1.