Sonocatalytic degradation of organic dyes and comparison of catalytic activities of CeO2/TiO2, SnO2/TiO2 and ZrO2/TiO2 composites under ultrasonic irradiation

The CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites were prepared by dispersing various nano-sized oxides (CeO₂, SnO₂, ZrO₂ and TiO₂) with ultrasound and mixing TiO₂ with CeO₂, SnO₂ and ZrO₂, respectively, in boiling water in a molar ratio of 4:1, followed by calcining temperature 500 °C for 60 min. Then a series of sonocatalytic degradation experiments were carried out under ultrasonic irradiation in the presence of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites and nano-sized TiO₂ powder. Also, the influences of heat-treatment temperature and heat-treatment time on the sonocatalytic activities of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites, and of irradiation time and solution acidity on the sonocatalytic degradation of Acid Red B were investigated by UV–vis spectra. It was found that the sonocatalytic degradation of Acid Red B shows significant variation in rate and ratio that decreases in order: CeO₂/TiO₂ > SnO₂/TiO₂ > TiO₂ > ZrO₂/TiO₂ > SnO₂ > CeO₂ > ZrO₂, and the corresponding ratios of Acid Red B in aqueous solution are 91.32%, 67.41%, 65.26%, 41.67%, 28.34%, 26.75% and 23.33%, respectively. And that the degradation ratio is only 16.67% under onefold ultrasonic irradiation. Because of the good degradation efficiency, this method may be an advisable choice for the treatment of non- or low-transparent wastewaters in the future.     

Sonocatalytic degradation of acid red B and rhodamine B catalyzed by nano-sized ZnO powder under ultrasonic irradiation

Nano-sized ZnO powder was introduced to act as the sonocatalyst after the treatment of high-temperature activation, and the ultrasound of low power was used as an irradiation source to induce nano-sized ZnO powder performing sonocatalytic degradation of acid red B and rhodamine B. At the same time, the effects of operational parameters such as solution pH value, initial concentration of dyestuff and addition amount of nano-sized ZnO powder have been examined in this paper. We found that the degradation ratios of acid red B and rhodamine B in the presence of nano-sized ZnO powder were much higher than that with only ultrasonic irradiation. However, the degradation ratio of acid red B was about two times higher than that of rhodamine B for the initial concentration of 10.0 mg/L, addition amount of 1.0 g/L nano-sized ZnO powder, solution acidity of pH 7.0 and 60 min irradiation experimental condition. The difference of the degradation ratios can be illustrated by the difference of chemical forms of acid red B and rhodamine B in aqueous solution and the surface properties of nano-sized ZnO particles. In addition, the researches on the kinetics of sonocatalytic reactions of acid red B and rhodamine B have also been performed and found to the follow pseudo first-order kinetics. All the experiments indicated that the sonocatalytic method in the presence of nano-sized ZnO powder was an advisable choice for the treatments of non- or low-transparent organic wastewaters in future.     

Sonocatalytic performance of Tb7O12/TiO2 composite under ultrasonic irradiation

A Tb(7)O(12)/TiO(2) composite was successfully synthesized through a hydrolysis-calcination process. The Tb(7)O(12)/TiO(2) composite catalyst was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, UV-Vis absorption/reflection spectroscopy, and X-ray diffraction (XRD). The heterogeneous sonocatalytic oxidation of amaranth in water, containing dispersed pure TiO(2) and Tb(7)O(12)/TiO(2) composite, was investigated under ultrasonic irradiation. The activity of the Tb(7)O(12)/TiO(2) catalyst is higher than that of pure TiO(2) during the sonodegradation of amaranth. The enhanced sonocatalytic activity of the composite may be attributed to the increase in charge separation efficiency and the presence of surface acidity.     

Sonocatalytic degradation and catalytic activities for MB solution of Fe treated fullerene/TiO2 composite with different ultrasonic intensity

Fe-fullerene/TiO(2) composite catalysts were prepared with titanium (IV) n-butoxide (TNB) by a sol-gel method. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), specific surface area (BET), X-ray diffraction analysis (XRD) and energy dispersive X-ray spectroscopy (EDX). The catalytic activities were evaluated by the catalytic oxidation of methylene blue (MB) solution. XRD patterns of the composites showed that the Fe-fullerene/TiO(2) composite contained a typical single and clear anatase phase. The surface properties shown by SEM present a characterization of the texture on Fe-fullerene/TiO(2) composites and showed a homogenous composition in the particles for the titanium sources used. The EDX spectra for the elemental identification showed the presence of C and Ti with strong Fe peaks for the Fe-fullerene/TiO(2) composite. The degradation of MB solution by ultrasonic irradiation in the presence of Fe-fullerene/TiO(2) compounds was investigated in complete darkness. With the increase in the amount of Fe, the degradation rate of methylene blue solution also increased.     

Sonocatalytic degradation of amaranth catalyzed by La3+ doped TiO2 under ultrasonic irradiation

The relationship between the physicochemical properties and the activity of sonocatalysts is investigated and elucidated in the sonodegradation of amaranth. The sonocatalyts are composed of La(3+) doped TiO(2) synthesized via a sol-gel process. The sonocatalysts are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopic analysis, UV-Vis absorption spectroscopy, and X-ray photoelectron emission spectroscopy. The sonodegradation products of amaranth are analyzed by UV-Vis absorption spectroscopy. The presence of the La(3+) doped TiO(2) catalysts substantially enhances the sonocatalytic degradation of amaranth in aqueous suspensions. The possible sonocatalytic mechanisms for such are discussed.     

Sonocatalytic degradation of methyl orange in the presence of TiO2 catalysts and catalytic activity comparison of rutile and anatase

Rutile and anatase titanium dioxide (TiO(2)) powders were used as sonocatalysts for the degradation of methyl orange which was used as a model compound. Ultrasound was used as an irradiation source. It was found that the sonocatalytic degradation ratios of methyl orange in the presence of TiO(2) powder were much better than ones without any TiO(2), but the sonocatalytic activity of rutile TiO(2) particles was obviously higher than that of anatase TiO(2) particles. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results show that the best degradation ratio of methyl orange can be obtained when the experimental conditions of the initial methyl orange concentration of 10 mg/l, rutile TiO(2) added amount of 500 mg/l, ultrasonic frequency of 40 kHz, output power of 50 W, pH=3.0 and 40 degrees C within 150 min were adopted. In addition, the catalytic activity of reused rutile TiO(2) catalyst was also studied and found to be better than new rutile TiO(2) catalyst sometimes. All experimental results indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO(2) powder was an advisable choice for treating non- or low-transparent organic wastewaters.     

Investigation on the sonocatalytic degradation of acid red B in the presence of nanometer TiO2 catalysts and comparison of catalytic activities of anatase and rutile TiO2 powders

Here, the nanometer anatase and rutile titanium dioxide (TiO(2)) powders were introduced to act as the sonocatalysts during the ultrasonic degradation of azo dye-acid red B which was chosen as model compound. The ultrasound of low power was used as an irradiation source to induce TiO(2) particles performing catalytic activity. It was found that the processes of sonocatalytic degradation were different between nanometer anatase TiO(2) and nanometer rutile TiO(2). For nanometer anatase TiO(2) catalyst, the acid red B was mainly oxidated by the holes on the surface of nanometer anatase TiO(2) particles, so that the decolorization and degradation happened at the same time. For the nanometer rutile TiO(2) catalyst, the acid red B was mainly oxidated by the *OH radicals from the ultrasonic cavitation, so that the decolorization of azo bond takes place primarily, and then the degradation of naphthyl ring does. The intermediates of acid red B in the presence of nanometer anatase and rutile TiO(2) powders have been monitored by UV-vis spectra and high performance liquid chromatography (HPLC), respectively. All experiments indicated that the degradation effect of acid red B in the presence of nanometer anatase TiO(2) powder was obviously better than that in the presence of nanometer rutile TiO(2) powder. Hence, the method of sonocatalytic degradation for organic pollutants in the presence of nanometer anatase TiO(2) powder is expected to be promising as an advisable choice for the treatment of organic wastewaters in future.     

Treatment of nano-sized rutile phase TiO2 powder under ultrasonic irradiation in hydrogen peroxide solution and investigation of its sonocatalytic activity

The treated mixed-crystal TiO(2) powder with high sonocatalytic activity was obtained through utilizing ultrasonic irradiation in hydrogen peroxide solution. At the same time, some influencing factors (including heat-treated temperature and heat-treated time) on the sonocatalytic activity of treated mixed-crystal TiO(2) powder were also considered through the degradation of methylene blue in aqueous solution. In this work, it was found that the sonocatalytic degradation ratio of methylene blue in the presence of treated mixed-crystal TiO(2) powder was much higher than ones in the presence of nano-sized rutile phase TiO(2) powder and with onefold ultrasonic irradiation. At last, the methylene blue in aqueous solution was completely degraded and became some simple inorganic anions such as NO(3)(-), SO(4)(2-) and Cl(-). All experiments indicated that the sonocatalytic method adopting treated mixed-crystal TiO(2) powder as sonocatalyst was an advisable choice for the treatments of non- or low-transparent wastewaters in future.     

MnO2/CeO2 for catalytic ultrasonic degradation of methyl orange

Catalytic ultrasonic degradation of aqueous methyl orange was studied in this paper. Heterogeneous catalyst MnO₂/CeO₂ was prepared by impregnation of manganese oxide on cerium oxide. Morphology and specific surface area of MnO₂/CeO₂ catalyst were characterized and its composition was determined. Results showed big differences between fresh and used catalyst. The removal efficiency of methyl orange by MnO₂/CeO₂ catalytic ultrasonic process was investigated. Results showed that ultrasonic process could remove 3.5% of methyl orange while catalytic ultrasonic process could remove 85% of methyl orange in 10 min. The effects of free radical scavengers were studied to determine the role of hydroxyl free radical in catalytic ultrasonic process. Results showed that methyl orange degradation efficiency declined after adding free radical scavengers, illustrating that hydroxyl free radical played an important role in degrading methyl orange. Theoretic analysis showed that the resonance size of cavitation bubbles was comparable with the size of catalyst particles. Thus, catalyst particles might act as cavitation nucleus and enhance ultrasonic cavitation effects. Measurement of H₂O₂ concentration in catalytic ultrasonic process confirmed this hypothesis. Effects of pre-adsorption on catalytic ultrasonic process were examined. Pre-adsorption significantly improved methyl orange removal. The potential explanation was that methyl orange molecules adsorbed on catalysts could enter cavitation bubbles and undergo stronger cavitation.     

Sonocatalytic degradation of tetracycline hydrochloride with CoFe2O4/g-C3N4 composite

In this work, different mass percent ratios of CoFe₂O₄ coupled g-C₃N₄ (w%-CoFe₂O₄/g-C₃N₄, CFO/CN) nanocomposites were integrated through a hydrothermal process for the sonocatalytic eradication of tetracycline hydrochloride (TCH) from aqueous media. The prepared sonocatalysts were subjected to various techniques to investigate their morphology, crystallinity, ultrasound wave capturing activity and charge conductivity. From the investigated activity of the composite materials, it has been registered that the best sonocatalytic degradation efficiency of 26.71 % in 10 min was delivered when the amount of CoFe₂O₄ was 25% in the nanocomposite. The delivered efficiency was higher than that of bare CoFe₂O₄ and g-C₃N₄. This enriched sonocatalytic efficiency was credited to the accelerated charge transfer and separation of e⁻-h⁺ pair through the S-scheme heterojunctional interface. The trapping experiments confirmed that all the three species i.e. ^•OH, h⁺ and ^•O₂⁻ were involved in the eradication of antibiotics. A strong interaction was shown up between CoFe₂O₄ and g-C₃N₄ in the FTIR study to support charge transfer as confirmed from the photoluminescence and photocurrent analysis of the samples. This work will provide an easy approach for fabricating highly efficient low-cost magnetic sonocatalysts for the eradication of hazardous materials present in our environment.     

表面修饰碳纳米管/二氧化钛复合光催化剂制备及催化活性研究

采用溶胶-凝胶法在聚乙烯吡咯烷酮(PVP)修饰的碳纳米管表面均匀沉积纳米级二氧化钛粒子制得复合光催化剂。采用透射电子显微镜(TEM)、X射线衍射仪(XRD)、紫外-可见吸收光谱仪(UV-Vis)和X射线光电子能谱仪(XPS)等手段对复合光催化剂进行表征。结果表明,二氧化钛粒子是呈球形、团聚,随机沉积在未修饰碳纳米管任意表面,甚至部分碳纳米管表面是完全裸露的。经PVP修饰后的碳纳米管,二氧化钛纳米粒子均匀沉积在碳纳米管表面,二氧化钛为纯锐钛矿晶体结构,没有金红石和板钛矿相。表面修饰碳纳米管/二氧化钛复合光催化剂在紫外光照射下降解亚甲基蓝,相比纯的二氧化钛和碳纳米管/二氧化钛复合光催化剂,具有非常高的催化活性。     

Sonophotocatalytic degradation of methyl orange by nano-sized Ag/TiO2 particles in aqueous solutions

Sonophotocatalytic behaviour of methyl orange (MeO) in aqueous solution illuminated by light generated by a xenon lamp was investigated. For all three kinds of photocatalysts: Degussa P25 (75% anatase, 25% rutile, with a surface area of 55.07 m(2)/g), Yili TiO(2) (mainly anatase, with a surface area of 10.45 m(2)/g) and Ag/TiO(2) (silver loaded on Yili TiO(2)), the degradation followed pseudo-first order kinetics. The results showed a synergistic effect between sonolysis and photocatalysis. Some parameters affecting the sonophotocatalytic degradation of MeO with nanoparticles Ag/TiO(2) were determined. The results indicated that the degradation ratio of MeO increased with the increase of ultrasonic power. An optimum 60 mg/L of Ag/TiO(2) added to relatively low concentrations of MeO was proved to have the most effective degradation efficiency. The study on the effects of hydroxyl radical (*OH) scavengers (i.e. mannitol and dimethyl sulfoxide) on the MeO degradation indicated that *OH radicals played an important role during MeO degradation, which enhanced MeO to be completely decomposed.     

Synergistic effects of C-Cr codoping in TiO2 and enhanced sonocatalytic activity under ultrasonic irradiation

C and Cr co-doped TiO₂ (C-Cr-TiO₂) sonocatalyst were synthesized by doping TiO₂ with glucose and CrCl₃ in a sol-gel method. The samples were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and X-ray photoelectron emission spectroscopy (XPS). C and Cr were detected by XPS analysis. The influence of dopants on the properties and sonocatalytic activity of TiO₂ was studied. The sonodegradation products of methylene blue were analyzed by UV-vis absorption spectroscopy. The presence of C-Cr-TiO₂ catalysts substantially enhanced the sonocatalytic degradation of MB in aqueous suspensions. The possible sonocatalytic mechanisms were also discussed.     

Synthesis and characterization of composite Au/TiO2 nanoparticles by laser irradiation

Composite Au/TiO₂ nanoparticles were synthesized by laser ablation of gold plate in TiO₂ sol. The nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The peak of surface plasmon is at 550 nm with a red shift of 30 nm compared with that of Au nanoparticles in water. Monolayers of composite Au/TiO₂ nanoparticles were obtained by dip-coating technique. The XRD pattern of Au/TiO₂ powders resembles a mixture of anatase TiO₂ and gold.     

Sonocatalytic degradation of Rhodamine B in the presence of C60 and CdS coupled TiO2 particles

CdS-TiO₂ and CdS-C₆₀/TiO₂ were prepared using C₆₀, cadmium acetate dehydrate [(CH₃COO)₂Cd·2H₂O], sodium sulfide (Na₂S·5H₂O) and titanium (IV) n-butoxide by a sol-gel method. The prepared sonocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). A rhodamine B (RhB) solution under ultrasonic irradiation was used to determine the catalytic activity. Excellent catalytic degradation of an RhB solution was observed using the CdS-C₆₀/TiO₂ composites under ultrasonic irradiation. C₆₀ coupled CdS-TiO₂ can enhance the Brunauer-Emmett-Teller (BET) surface area and increase the decolorization rate for rhodamine B solution. The results also shows that increase the content of CdS can enhance the catalytic activity.     

Sonodegradation and photodegradation of methyl orange by InVO4/TiO2 nanojunction composites under ultrasonic and visible light irradiation

The InVO₄/TiO₂ nanojunction composites with different weight ratio of 1:10, 1:25, 1:50 and 1:100 were successfully constructed using an ion impregnate method, followed by calcining temperature 400 °C for 2 h in Ar. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were evaluated through the degradation of methyl orange (MO) in aqueous solution under ultrasonic and visible light irradiation, respectively. The experimental results determined that the (1:50) InVO₄/TiO₂ nanojunction composite has exhibited the highest sonocatalytic activity. It can be ascribed to vectorial charge transfer at the co-excited InVO₄/TiO₂ interface under ultrasonic irradiation, results in the complete separation of electrons and holes. Interestingly, the (1:25) InVO₄/TiO₂ nanojunction composite displayed superior photocatalytic activity for MO degradation under visible light, indicating that InVO₄ as a narrow band gap sensitizer can expand photocatalytic activity of TiO₂ to visible region, and the charge transfer can be formed from high energy level of InVO₄ conduction band to the low energy level of TiO₂ conduction band in a present of excited InVO₄ alone under visible light irradiation. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were found to be dependent significantly on different InVO₄ contents, which can be explained by the influence of charge transfer on the basis of the work functions of different catalysis mechanism.     

Magnetic properties of Sn-substituted Ni-Zn ferrites synthesized from nano-sized powders of NiO,ZnO, Fe_2O_3, and SnO_2

A series of Ni_(0.6-x/2)Zn_(0.4-x/2)Sn_xFe_2O_4(x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.3)(NZSFO) ferrite composities have been synthesized from nano powders using a standard solid state reaction technique. The spinel cubic structure of the investigated samples has been confirmed by x-ray diffraction(XRD). The magnetic properties such as saturation magnetization(M_s),remanent magnetization(M_r), coercive field(H_c), and Bohr magneton(μ) are calculated from the hysteresis loops. The value of M_s is found to decrease with increasing Sn content in the samples. This change is successfully explained by the variation of A-B interaction strength due to Sn substitution in different sites. The compositional stability and quality of the prepared ferrite composites have also been endorsed by the fairly constant initial permeability(μ') over a wide range of frequency. The decreasing trend of μ' with increasing Sn content has been observed. Curie temperature TChas been found to increase with the increase in Sn content. A wide spread frequency utility zone indicates that the NZSFO can be considered as a good candidate for use in broadband pulse transformers and wide band read-write heads for video recording. The composition of x = 0.05 shows unusual results and the possible reason is also mentioned with the established formalism.     

Effect of coal ash on hydrazine degradation under stirring and ultrasonic irradiation conditions

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1-5.0 mmol/L was investigated as a function of amount of coal ash (0.0-5.0 wt%) under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the rate of decrease in the hydrazine concentration depended upon an amount of coal ash under the stirring and ultrasonic irradiation condition. It was considered under the stirring condition that hydrazine was adsorbed and degraded partly on coal ash. Furthermore, the sonochemically formed OH radicals were more effective in the hydrazine degradation than stirring condition in the presence of an intermediate amount of coal ash (0.6-2.4 wt%), whereas the effect of OH radicals disappeared in the presence of coal ash more than 2.4 wt%.     

Comparison of catalytic activities for photocatalytic and sonocatalytic degradation of methylene blue in present of anatase TiO2-CNT catalysts

Anatase TiO(2)-CNT catalysts with high specific surface areas were prepared by depositing TiO(2) particles on the surface of carbon nanotubes (CNTs) using a modified sol-gel technique. These catalysts prepared with different amounts of CNTs were characterized by nitrogen adsorption, Fourier Transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray (EDX) and ultraviolet-visible (UV-Vis) spectroscopy. The catalytic activity of the anatase TiO(2)-CNT catalysts was assessed by examining the degradation of methylene blue (MB) from model aqueous solutions as a probe reaction under visible light and ultrasonic irradiation. The synergistic effect of the greater surface area and catalytic activities of the composite catalysts was examined in terms of the strong adsorption ability and interphase interaction by comparing the different amounts and roles of CNTs in the catalysts.     

Enhanced photocatalytic performance of ultrasound treated GO/TiO2 composite for photocatalytic degradation of salicylic acid under sunlight illumination

The current research work deals with the preparation of TiO₂ and GO/TiO₂ composite by simple, chemical, cost effective hydrothermal method. Graphene oxide (GO) is prepared by modified Hummer’s method. Dispersion of GO is achieved by an ultrasonic cleaning bath for 1 h. using a power of 200 W and at a frequency of 40 kHz. The prepared catalyst material is characterized by different characterization techniques. XRD study confirms the prepared material is polycrystalline in nature. The synthesized TiO₂ and GO/TiO₂ photocatalyst materials are used to study the photocatalytic degradation of salicylic acid under sunlight illumination. GO/TiO₂ composite shows superior photocatalytic activity than TiO₂. GO/TiO₂ composite shows 57% degradation of salicylic acid. Mineralization of salicylic acid is studied using chemical oxygen demand.