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As a newly emerging catalysis, tribocatalysis is receiving more and more attention with regard to the criteria to fabricate or choose materials as catalysts for it. In this study, two different commercial silicon (Si) powders, Si30 and Si300, were adopted as catalysts in tribocatalytic degradation of organic dyes. Only round nanoparticles from 30 to 100nm were observed in Si30, while some highly large and irregular particles, as large as 1000nm × 500nm and with a roughly flat major surface, could be observed in Si300. Stimulated through magnetic stirring using Teflon magnetic rotary disks, as much as 95% of 20 mg/L rhodamine B (RhB) solution and 97% of 20 mg/L methyl orange (MO) solution were degraded by Si300 after 3h and 50min, respectively; while only 73% of RhB and 83% of MO were degraded by Si30 after 5h and 4h, respectively. EPR spectra showed that more superoxide and hydroxyl radicals were generated by Si300 under magnetic stirring. It is proposed that in those large particles in Si300, their large flat major surfaces dramatically enhance their absorption of mechanical energy through friction and there are much less lattice defects to hinder electrons and holes from diffusing to the surface, which both results in the contrasting tribocatalytic degradations of organic dyes between Si300 and Si30. These findings reveal a huge difference in tribocatalytic performance among different materials of the same composition.

This paper reports the enhancement in the sensing properties of organic dye methyl orange (MO) by introducing TiO₂ nanoparticles. For this purpose, two surface type Ag/MO/Ag and Ag/MO:TiO₂/Ag multifunctional sensors were fabricated by spin coating a 3.0 wt.% solution of MO and 3.0:0.3 wt.% of MO:TiO₂ composite on pre-patterned silver (Ag) electrodes. The gap between Ag electrodes was 40 μm. The Ag/MO/Ag and Ag/MO:TiO₂/Ag structures were characterized to investigate their response towards humidity and temperature variations. The Ag/MO:TiO₂/Ag sensor exhibited better sensitivity and response time than Ag/MO/Ag sensor. The large surface to volume ratio of TiO₂ nanoparticles is the primary reason for the higher sensitivity of Ag/MO:TiO₂/Ag sensor. The sensors can be used to detect humidity variations from 30% to 95% RH and temperature variation from 30°C to 200°C with good stability. Surface morphologies of the film were investigated by scanning electron microscope (SEM).

Transition metal oxide photocatalysis is a relatively new method representing advanced oxidation process to be applied in industrial wastewater treatment especially for degradation of organic pollutants. We investigate TiO₂ as a photocatalyst for the photocatalytic degradation of Rhodamine B (RhB) under simulated sunlight. Various parameters and their effectiveness have been studied. The effects of processing parameters including catalyst loading and feed concentration were investigated; and the degradation pathway was proposed based on the UHPLC-MS analysis. The result showed that a higher kinetic rate can be obtained by employing low catalyst loading and feed concentration, i.e., 0.5 g/L of TiO₂ loading and 5 ppm of RhB concentration, respectively. For this particular system, the optimum degradation rate ($k$) can achieve 0.297/min. The effectiveness of solar light-TiO₂ system for RhB degradation shows this method can be used for wastewater treatment.

Nanostructured zero-valent iron (NSZVI) particles were synthesized by the method of ferric ion reduction with sodium borohydride with subsequent drying and passivation at room temperature in technical grade nitrogen. The obtained sample was characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering studies. The prepared NSZVI particles represent 100–200nm aggregates, which consist of 20–30nm iron nanoparticles in zero-valent oxidation state covered by thin oxide shell. The reactivity of the NSZVI sample, as the removal efficiency of refractory azo dyes, was investigated in this study. Two azo dye compounds, namely, orange G and methyl orange, are commonly detected in waste water of textile production. Experimental variables such as NSZVI dosage, initial dye concentration and solution pH were investigated. The kinetic rates of degradation of both dyes by NSZVI increased with the decrease of solution pH from 10 to 3 and with the increase of NSZVI dosage, but decreased with the increase of initial dye concentration. The removal efficiencies achieved for both orange G and methyl orange were higher than 90% after 80min of treatment.

This work presents an important analysis and comparative study between two organic waste rhodamine B (RhB) and methyl orange (MO) dyes as pollutant models degeneration under sunlight. Hematite ($\alpha$-Fe₂O₃) nanorods were synthesized and deposited on glass substrates using an efficient and simple one-step hydrothermal method. The nanorods were characterized by XRD, FESEM, EDX, and UV–Vis equipment. The photodegeneration parameters of $\alpha$-Fe₂O₃ films were calculated by modeling the photodegradation of MO and RhB dyes as pollutants under sunlight irradiation for 150min. Results revealed that the degradation efficiency of $\alpha$-Fe₂O₃ films of MO and RhB dyes was 72.7% and 91.9%, respectively. The optimized photocatalyst degraded RhB more efficiently than the MO solution.

Palygorskite (denoted as Pal) was used as an economical carrier of hybrid photocatalyst TiO₂–Fe_xO_yvia an in situ depositing technique (marked as Pal–TiO₂–Fe_xO_y). The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), brunner-emmet-teller (BET) measurements, X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectra measurements. Results showed that TiO₂–Fe_xO_y composite particles with average size of about 10 nm were loaded onto the Pal fibers' surface. Fe_xO_y acted not only as magnetic source but also took part in the formation of TiO₂–Fe_xO_y heterojunction structure, which resulted in the obvious absorption in visible light region for the obtained Pal–TiO₂–Fe_xO_y composite photocatalyst. The obtained Pal–TiO₂–Fe_xO_y shows excellent photocatalytic activity toward photodegradation of Methyl orange (MO) under visible light irradiation and the degradation ratio reached 94% within 180 min. Moreover, Pal–TiO₂–Fe_xO_y could be readily recovered from the reaction solution by the magnet. Possible mechanism for the enhancement was also proposed.

In this research, a series of novel MoSe₂/SrTiO₃ heterostructures were successfully prepared by a two-step hydrothermal method. The samples were characterized by XRD, UV-Vis, SEM, TEM, EDS and XPS. Results showed that the degradation of MO under UV is better than that under the visible light. And, MoSe₂ loaded on SrTiO₃ under UV irradiation demonstrated a higher catalytic activity. The degradation rate of methyl orange was 99.46% for MoSe₂/SrTiO₃ under the optimum loading weight (0.1wt.%). This is mainly because the combination of MoSe₂ and SrTiO₃ prevents electrons and holes recombination in SrTiO₃ and $\cdot$O${}_2^{-}$ appears in the system. In general, MoSe₂/SrTiO₃ heterostructures have good environmental friendliness for photocatalytic degradation.

In this study, LaFeO₃/ZnIn₂S₄ composites were synthesized via in situ synthesis. The composition, structure and optical absorption properties of LaFeO₃/ZnIn₂S₄ were characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy, fluorescence spectroscopy (PL), Fourier Transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The photocatalytic activity of the LaFeO₃/ZnIn₂S₄ photocatalyst was determined based on the degradation of methyl orange (MO). LaFeO₃/ZnIn₂S₄ composites showed much better photocatalytic performance compared with pure LaFeO₃ and ZnIn₂S₄. The enhanced photocatalytic performance was attributed to intimately contacted interfaces and charge transfer channels which can effectively transfer and separate the photogenerated charge carriers.

Metal-ferrite/maghemite nanocomposites (NiFe₂O₄/***$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O${}_3)$ were synthesized via doping maghemite with metal salt (NiCl₂ or CoCl${}_2)$ followed by reduction of metal ions using NaBH₄. The synthesized metal-ferrite/maghemite nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) and the amounts of the dopant-metal (Ni/Co) were determined using ICP-OES technique. Results showed that this synthetic route produced nanocomposites with highly active ferrite phases MFe₂O₄. The synthesized nanocomposites exhibited exceptional catalytic activities for the reduction of 4-nitrophenol and 2-nitroaniline as well as the catalytic degradation of methyl orange. Specific activity parameter of NiFe₂O₄/$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O₃ toward reduction of 4-NP reached 993.9 and 929.8s${}^{-1}$g${}_{\mathrm{\text{metal}}}^{-1}$, respectively. These high values of specific activities are higher than most reported metal-ferrite composites prepared via traditional co-precipitation methods. Besides, strong magnetic properties of the prepared metal-ferrite/maghemites facilitates easy separation process for several reuses.

The WSe₂/g-C₃N₄ (graphite carbon nitride) composite with photocatalytic properties was synthesized using a hydrothermal method. This synthesis pathway can be characterized by being simple, inexpensive and nonpolluting, integrating the concept of green chemistry. The WSe₂/g-C₃N₄ composite could effectively degrade methyl orange solution under visible light irradiation. The decolorization experiment of methyl orange solution shows that the degradation rate of the 30wt.% WSe₂/g-C₃N₄ composite can reach 98.7% after 100min of illumination, while the degradation rate of pure g-C₃N₄ was only 87.6% under the same conditions. This can be attributed to the fact that the combination of WSe₂ and g-C₃N₄ nanosheets can increase the number of active binding sites, increasing the rate of charge separation and transport ability, decreasing the recombination rate of the photogenerated electron–hole pairs. Therefore, the WSe₂/g-C₃N₄ composite will have potential development as a new material with low cost, easy synthesis and excellent performance in photocatalytic degradation of water pollution.

Nd-doped TiO₂ mesoporous microspheres with possessing regular micro/nanostructure were synthesized by a simple and facile method. The structure and optical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption isotherms and UV-Visible absorbance spectroscopy. It was revealed that Nd-doped TiO₂ mesoporous microspheres are composed of primary nanoparticles with a particle size of $\sim$25nm. The photocatalytic activities of all the samples were evaluated by degradation methyl orange (MO) in aqueous solution as a model reaction under xenon lamp light irradiation. The results showed that the doped samples demonstrated a higher photocatalytic activity than TiO₂ mesoporous microspheres, and the MO of 10mg/mL almost could be completely degraded by the Nd-doped TiO₂ mesoporous sample (the dosage of Nd salt to TiO₂ is 6%) under xenon lamp light irradiation within 1h.

AgI/4A molecular sieves photocatalysts with different mass ratios were prepared by depositing the silver iodide on the 4A molecular sieve by ion exchange method. When the mass ratio of silver iodide and 4A molecular sieve was 2:1, AgI/4A molecular sieves exhibited enhancing photocatalytic activity than pure AgI and 4A molecular sieves. The degradation rate of methyl orange (MO) dye reached 96.4% at 20 min. The possible mechanism of photodegradation by AgI/4A molecular sieves was proposed.

AgI/4A molecular sieves photocatalysts with different mass ratios were prepared by depositing the silver iodide on the 4A molecular sieve by ion exchange method. When the mass ratio of silver iodide and 4A molecular sieve was 2:1, AgI/4A molecular sieves exhibited enhancing photocatalytic activity than pure AgI and 4A molecular sieves. The degradation rate of methyl orange (MO) dye reached 96.4% at 20 min. The possible mechanism of photodegradation by AgI/4A molecular sieves was proposed.