Pengpeng Qiu

Uniform core–shell structured magnetic mesoporous TiO2 nanospheres as a highly efficient and stable sonocatalyst for the degradation of bisphenol-A

Uniform core–shell structured magnetic mesoporous TiO2 (Fe3O4@SiO2@mTiO2) nanospheres were fabricated via a kinetically controlled Stober method. A silica interlayer with a thickness of ∼25 nm was introduced as a passivation barrier to prevent photodissociation, as well as increase the thermal stability of the core–shell materials. After crystallizing at 600 °C under nitrogen, the resultant nanospheres (Fe3O4@SiO2@mTiO2-600) possessed well-defined core–shell structures with a high magnetic susceptibility (∼17.0 emu g−1) and exhibited uniform mesopores (∼5.2 nm), large BET surface area (∼216 m2 g−1) and large pore volume (∼0.20 cm3 g−1). More importantly, the magnetic mesoporous TiO2 was demonstrated for the first time as a highly efficient and stable sonocatalyst for the degradation of bisphenol-A. The pseudo first-order-reaction constant of the magnetic mesoporous TiO2 was measured to be 0.164 min−1, which is 1.49 and 2.27 times higher than that of P25 and ultrasound alone, respectively. The remarkable performance is attributed to the fast mass diffusion, large adsorption rate and enhanced hydroxyl-radical-production rate of the nanospheres. More importantly, the catalyst can be easily recycled within 2 minutes using an external magnetic field, and a constant catalytic activity is retained even after eight cycles. This study paves a promising way for the design and synthesis of magnetically separable sonocatalysts for the degradation of organic pollutants, which is of significant importance for practical applications from both environmental and industrial points of view.

Application of Box-Behnken design with response surface methodology for modeling and optimizing ultrasonic oxidation of arsenite with H2O2

AbstractA combined ultrasound (US)/H2O2 process was used to oxidize arsenite to arsenate, yielding a synergistic effect value of 1.26. This showed that the combined process could be an effective method of oxidizing arsenite, instead of using either ultrasonic or H2O2 oxidation processes. This combined process was successfully modeled and optimized using a Box-Behnken design with response surface methodology (RSM). The effects of the US power density, the initial concentration of arsenite, and the H2O2 concentration on the sonochemical oxidation efficiency of arsenite were investigated. Analysis of variance indicated that the proposed quadratic model successfully interpreted the experimental data with coefficients of determination of R2 = 0.95 and adjusted R2 = 0.91. Through this model, we can predict and control the oxidation efficiency under different conditions. Furthermore, the optimal conditions for the oxidation of arsenite were found to be a US power density of 233.26 W L−1, an initial arsenite concentration of 0.5 mg L−1, and an H2O2 concentration of 74.29 mg L−1. The predicted oxidation efficiency obtained from the RSM under the optimal conditions was 88.95%. A confirmation test of the optimal conditions verified the validity of the model, yielding an oxidation efficiency of 90.1%.

Ordered mesoporous C/TiO2 composites as advanced sonocatalysts

Ordered mesoporous C/TiO2 composites have been fabricated via an evaporation induced co-assembly method, and demonstrated as a highly efficient sonocatalyst. The effects of the carbon content in the composites and calcination temperature have been investigated thoroughly in this work and optimized for the production of well-defined mesoporous C/TiO2 materials. The resultant composites possess superior “brick–mortar” frameworks with uniform TiO2 nanocrystals glued by a carbon matrix, and exhibit highly ordered mesostructures with high surface area (∼200 m2 g−1). More importantly, the mesoporous C/TiO2 composites show a high sonocatalytic degradation rate of Rhodamine B. The maximum pseudo-first-order reaction rate constant obtained with the composites 15C–85TiO2-450 (C: 15.2 wt%, TiO2: 84.8 wt%, calcined at 450 °C) is 0.178 min−1, which is 2.7 and 4.8 times higher than that of P25 (0.062 min−1) and ultrasound (0.037 min−1) alone, respectively. The excellent sonocatalytic performance is a result of fast mass diffusion, enhanced nucleation rate and rapid surface hydroxyl radical oxidation. In addition, the recycling test shows that the sonocatalytic degradation rate with 15C–85TiO2-450 is retained even after five cycles, which is related to the well-retained mesostructure with superior mechanical stability. We believe that the present results provide important insights into the design and synthesis of advanced sonocatalysts.

Mesoporous TiO2 encapsulating a visible-light responsive upconversion agent for enhanced sonocatalytic degradation of bisphenol-A

Herein, we report the integration of a visible-light active upconversion agent (Er:Y2O3) with mesoporous TiO2 via a modified two-step sol–gel coating method. The resultant material possesses a well-defined core–shell structure with a good upconversion property and exhibits uniform worm-like mesopores (∼3.8 nm), a high BET surface area (∼151.5 m2 g−1) and a large pore volume (∼0.23 cm3 g−1). The composite was demonstrated as an advanced sonocatalyst, showing a superior degradation performance for bisphenol-A (BPA). The effect of the erbium dopant content on the upconversion property and sonocatalytic performance was evaluated for the production of the best sonocatalyst. We found that the maximum pseudo first-order reaction rate constant in the presence of the composite with an Er3+ content of 3 wt% in Y2O3 nanocrystals is calculated to be 0.155 min−1, which is 2.9 and 2 times larger than that of US alone (0.054 min−1) and hollow structured mesoporous TiO2 (0.077 min−1), respectively. More importantly, the degradation rate is much higher than that of the sonocatalysts reported previously for treatment of BPA (0.09–0.14 min−1). The superior catalytic activity can be attributed to an intensified cavitation reaction zone and an enhanced amount of photo-generated charges. Moreover, the recycling test shows that a constant catalytic activity is retained even after 4 cycles. This study paves a promising way for the development of a multi-functional catalyst for sonochemical processes.

Facile synthesis of uniform yolk–shell structured magnetic mesoporous silica as an advanced photo-Fenton-like catalyst for degrading rhodamine B

Through an ultrasound assisted etching method, uniform yolk–shell structured magnetic mesoporous silica (Fe3O4@void@mSiO2) nanospheres have been fabricated and for the first time demonstrated as an efficient catalyst for degrading rhodamine B under photo-Fenton-like conditions.

Magnetic Pd@Fe3O4 composite nanostructure as recoverable catalyst for sonoelectrohybrid degradation of Ibuprofen

In the present research, the degradation of an emerging pharmaceutical micro-pollutant, Ibuprofen (IBP) by using Pd@Fe3O4 and a hybrid sono-electrolytical (US/EC) treatment system has been demonstrated for the first time. The magnetically separable nanocomposite, Pd@Fe3O4 catalyst was synthesized following co-precipitation method to enhance the efficiency of US/EC system. The synthesized catalyst showed a strong reusable property even after applying for five times and in all the five cases, 100% degradation of IBP was maintained. It not only enhanced the IBP degradation rate, but also reduced the energy consumption of the system by ∼35%. Its strong magnetization value of 64.27emug-1 made it easily separable. Hence, a comprehensive knowledge on the application of combined energy based US/EC system and magnetically separable multifunctional catalysts for degradation of intractable pollutants like Ibuprofen was achieved, assuring that US/EC can be an effective option for IBP treatment.

A review on heterogeneous sonocatalyst for treatment of organic pollutants in aqueous phase based on catalytic mechanism

Heterogeneous sonocatalysis, as an emerging advanced oxidation process (AOP), has shown immense potential in water treatment and been widely demonstrated to remove persistent organic compounds in the past decade. The present article aims to provide a comprehensive review on the development of a heterogeneous catalyst for enhancing the ultrasonic degradation rate of organic pollutants from a viewpoint of sonocatalytic mechanism. The rational design and fundamentals for preparing sonocatalysts are presented in the context of facilitating the heterogeneous nucleation and photo-thermal-catalytic effects as well as considering the mechanical stability and separation capacity of the heterogeneous catalyst. In addition, some new trends, ongoing challenges and possible methods to overcome these challenges are also highlighted and proposed.

Facile synthesis of uniform magnetic graphitic carbon for an efficient adsorption of pentachlorophenol

Uniform core–shell structured magnetic graphitic carbon (Fe3O4@SiO2@g-C) nanospheres were fabricated via a two-step Stober coating strategy, followed by a carbonization process in N2 atmosphere. The resultant composites possess a large magnetic susceptibility (25 emu g−1) and a high graphitization degree, making it an excellent magnetically separable adsorbent for the removal of pentachlorophenol.