Preparation of Zr/Y co-doped TiO2 photocatalyst and degradation performance of hydroquinone

Fabrication of poly (quinine-co-itaconic acid) incorporated reduced graphene oxide nanocomposite and its application for electrochemical sensing and photocatalysis of hydroquinone

In this work, we report the synthesis of poly (quinine-co-itaconic acid) incorporated graphene oxide composite that is electro-active and photo-active simultaneously. The poly (quinine-co-itaconic acid)@rGO composite was successfully utilized for electrochemical detection and photocatalytic degradation of hydroquinone (HQ). HQ is recognized as an environmental pollutant because of its high toxicity to human health even at low concentrations. The synthesized composite was characterized using different characterization techniques i.e. Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD), Brunauer-Emmett-Teller (BET) and zeta potential. The characterization studies revealed the net negative surface charge of -17.6 mV for poly (quinine-co-itaconic acid)@rGO composite that confirms its stability. Moreover, the XRD and FTIR studies confirmed the fabrication of poly (quinine-co-itaconic acid)@rGO composite. The electrochemical properties of synthesized composite were determined via cyclic voltammetry and electrochemical impedance spectroscopy which showed high conductivity and charge transfer kinetics. Under optimized condition, the sensor showed excellent response for hydroquinone i.e. potential window from -0.6 to 0.6 V at scan rate 50 mV s-1 and borate buffer of pH 8 as supporting electrolyte. The developed method was comprehensively validated and found linear between 0.1 to 40 μM of HQ, with limit of detection 0.03 μM and limit of quantification 0.1 μM, respectively. The real water and personal care products samples were used to check the applicability of developed sensor and good percent recovery was achieved. The synthesized poly (quinine-co-itaconic acid)@rGO composite was also utilized for photocatalytic degradation of HQ and the degradation efficiency was obtained as 99% with dosage of 0.5 g L-1 under optimized conditions such as solution pH 7, initial concentration of HQ 10 mg L-1, catalyst dosage of 5 mg and irradiation time of 40 min, respectively. The degradation efficiency of poly (quinine-co-itaconic acid)@rGO composite was also evaluated in real water samples from industry and river.

Hydrodynamic cavitation degradation of hydroquinone using swirl-type micro-nano bubble reactor

This study reports the degradation of hydroquinone using lab-scale hydrodynamic cavitation approach (aswirl-type micro-nano bubble reactor), which is considered a green and effective method. The effects of inlet pressure, gas flow rate, pH and initial hydroquinone concentration on hydroquinone degradation were analysed based on experimental research. After experiments investigation, it was concluded that with pH 7.38, hydroquinone concentration of 50 mg/L, and int pressure of 0.2 MPa, the degradation efficiency of hydroquinone reached 91.25% in wastewater. Furthermore, this study also investigated the degradation effect of hydroquinone wastewater by hydrodynamic cavitation combined with persulfate oxidation (HC + PS). The kinetics of hydroquinone degradation by HC or PS oxidation alone and HC + PS oxidation were also examined. Compared with the degradation method alone, the degradation of hydroquinone by HC + PS was more pronounced, and the enhancement factor was 4.55, which indicates that HC greatly enhances the oxidation capacity of PS. In additon, from viewpoint of energy consumption and operating cost, the synergy of HC + PS (1.05 mM) is also the most promising combination. Based on the detection results of the Gas chromatography-mass spectrometry (GC-MS) the possible degradation pathways of hydroquinone were analysed: under the action of ·OH and the high temperature and pressure by cavitation process, the hydroquinone molecule undergoes dehydrogenation and ring-opening reaction, demethylation and decarboxylation reaction to produce intermediate products, which are finally converted into CO2 and H2O in micro-nano bubble cavitation process.

ZIF-67 and Biomass-Derived N, S-Codoped Activated Carbon Composite Derivative for High-Effective Removal of Hydroquinone from Water

Hydroquinone (HQ) in wastewater is of great concern, as it is harmful to human health and threatens the ecological environment. However, the existing adsorbents have low adsorption capacity for HQ. To improve the removal of HQ, N,S-codoped activated carbon-ZIF-67 (NSAC-ZIF-67@C) was synthesized in this study by in situ growth of ZIF-67 on N,S-codoped activated carbon (NSAC) and carbonization. The influence of pH, contact time, and initial concentration on the adsorption behaviors of NSAC-ZIF-67@C on HQ were investigated. Owing to the synergistic effect of abundant active sites and well-developed pore structure, the NSAC-ZIF-67@C achieved a prominent adsorption capacity of 962 mg·g-1 and can still retain high adsorption performance after 5 cycles for HQ, which is superior to that of reported other adsorbents. HQ adsorption follows the pseudo-second-order kinetics model (R2 = 0.99999) and the Freundlich isotherm model. X-ray photoelectron spectroscopy (XPS) analysis before and after adsorption as well as density functional theory (DFT) calculation results showed that pyridinic-N-termini were conducive to the π-π interactions and hydrogen-bonding interactions. Therefore, the adsorption mechanisms of NSAC-ZIF-67@C on HQ involve pore filling, electrostatic attraction, π-π interaction, and hydrogen bonding. This study is expected to provide a reference for designing highly effective adsorbents for wastewater treatment.

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Unraveling the impact of microwave-assisted techniques in the fabrication of yttrium-doped TiO2 photocatalyst

In this study, we investigate the role of microwave technology in the fabrication of yttrium-doped TiO2 through a comparative analysis of hydrothermal techniques. Microwave-assisted hydrothermal synthesis offers advantages, but a comprehensive comparison between microwave-assisted and conventional methods is lacking. Therefore, in our investigation, we systematically evaluate and compare the morphological, structural, and optical properties of yttrium-doped TiO2 samples synthesized using both techniques. The X-ray diffraction (XRD) patterns confirm the anatase tetragonal structure of the synthesized TiO2-Y systems, while the larger ion radius of yttrium (Y3+) compared to titanium (Ti4+) presents challenges for yttrium to incorporate into the TiO2 lattice. The X-ray Photoelectron Spectroscopy (XPS) revealed a significant difference in the atomic content of yttrium between the TiO2-Y systems synthesized using microwave-assisted and conventional methods. This finding suggests that the rapid microwave method is more effective in successfully doping TiO2 with rare earth metals such as yttrium. The photo-oxidation of carbamazepine (CBZ) using TiO2-Y systems demonstrated high efficiency under UV-LED light. Microwave-synthesized TiO2-Y demonstrates improved photo-oxidation efficiency of CBZ, attributed to enhanced absorption, charge transfer, surface area, and crystallite size. Overall, the microwave-synthesized TiO2-Y systems showed promising performance for the photo-oxidation of CBZ, with improved efficiency compared to conventional synthesis methods.

Synergistic Effect of Y Doping and Reduction of TiO2 on the Improvement of Photocatalytic Performance

Pure TiO2 and 3% Y-doped TiO2 (3% Y-TiO2) were prepared by a one-step hydrothermal method. Reduced TiO2 (TiO2-H2) and 3% Y-TiO2 (3% Y-TiO2-H2) were obtained through the thermal conversion treatment of Ar-H2 atmosphere at 500 °C for 3 h. By systematically comparing the crystalline phase, structure, morphological features, and photocatalytic properties of 3% Y-TiO2-H2 with pure TiO2, 3% Y-TiO2, and TiO2-H2, the synergistic effect of Y doping and reduction of TiO2 was obtained. All samples show the single anatase phase, and no diffraction peak shift is observed. Compared with single-doped TiO2 and single-reduced TiO2, 3% Y-TiO2-H2 exhibits the best photocatalytic performance for the degradation of RhB, which can be totally degraded in 20 min. The improvement of photocatalytic performance was attributed to the synergistic effect of Y doping and reduction treatment. Y doping broadened the range of light absorption and reduced the charge recombination rates, and the reduction treatment caused TiO2 to be enveloped by disordered shells. The remarkable feature of reduced TiO2 by H2 is its disordered shell filled with a limited amount of oxygen vacancies (OVs) or Ti3+, which significantly reduces the Eg of TiO2 and remarkably increases the absorption of visible light. The synergistic effect of Y doping, Ti3+ species, and OVs play an important role in the improvement of photocatalytic performances. The discovery of this work provides a new perspective for the improvement of other photocatalysts by combining doping and reduction to modify traditional photocatalytic materials and further improve their performance.

Study on the preparation of molecularly imprinted ZrO2-TiO2 photocatalyst and the degradation performance of hydroquinone

In this paper, molecularly imprinted Zr-doped TiO2 photocatalysts (MIP-ZrO2-TiO2) were prepared by the molecularly imprinted sol-gel method for the photocatalytic degradation study of hydroquinone (HQ) as the target pollutant. For the effectiveness of the MIP-ZrO2-TiO2 catalyst in degrading HQ, the effects of Zr doping ratio, imprinted molecule dosage, calcination conditions, and pollutant concentration on its photocatalytic activity were investigated. XRD, TEM, XPS, and other techniques were used to evaluate the materials, and the findings revealed that MIP-ZrO2-TiO2 films with imprinted HQ were successfully produced on the ZrO2-TiO2 surface. The optimal preparation conditions were n(Ti):n(Zr) = 100:8, m(HQ) = 1.5 g, 550 °C for the calcination temperature, and 2 h for the calcination duration. The optimum reaction conditions were 10 mg/L HQ concentration, 1 g/L catalyst dose, and a pH of 6.91. According to the findings of photocatalytic tests, during 30 min of UV lamp (365 nm) irradiation, the degradation rates of MIP-ZrO2-TiO2, ZrO2-TiO2, and TiO2 for HQ were 90.58%, 83.94%, and 58.30%, respectively. The findings revealed that the doping of Zr metal and the addition of imprinted molecules improved the photocatalytic activity of TiO2, which can be used for the efficient treatment of low concentrations of hard-to-degrade hydroquinone.

In situ generation of hydroxyl radicals by B-doped TiO2 for efficient photocatalytic degradation of acetaminophen in wastewater

Acetaminophen (AP) is a widely used antipyretic analgesic belonging to the class of PPCPs, which is difficult to be effectively degraded by traditional water treatment processes. However, photocatalytic technology may be an effective approach. Herein, B-doped TiO₂ photocatalytic materials were synthesized by sol-gel method, calcinated at 600℃ for 2 h, investigated by XRD, TEM, XPS, and other characterization methods. The photocatalytic efficiency and factors affecting the photocatalytic activity were assessed by degradation of AP under 365 nm UV light. Compared with undoped TiO₂, 4%B-TiO₂ nanopowder has smaller grain size, higher porosity, and lower bandgap energy of 3.11 eV. Scavenging experiments and ESR results show that •OH is the principal active species. Hence, the degradation efficiency of AP is as high as 98.8% in 30 min when adopting 10-mg/L AP initial concentration and 1-g/L 4%B-TiO₂ loading, owing to efficient •OH generated by B-TiO₂.