Facile sonochemical synthesis of Ag2O-guar gum nanocomposite as a visible light photocatalyst for the organic transformation reactions

Silver Oxide (Ag₂O)-Guar gum nanocomposite was fabricated via a simple sonochemical co-precipitation method. The obtained photocatalyst was characterized with various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, scanning electron microscopy and transmission electron microscopy along with energy dispersion X-ray spectroscopy. The findings have demonstrated that Ag₂O nanoparticles are spherical of 5-20 nm and were dispersed on the surface of polysaccharide guar gum to form Ag₂O-guar gum nanocomposite. The as-synthesized nanocomposite was enacted as a competent photocatalyst for the reduction of nitrobenzene and oxidation of benzyl alchohol. The conversion efficiency for the reduction of nitrobenzene was 96 % with the addition of sodium borohydride, and the conversion of benzyl alcohol was 98 %. The highly efficient photocatalytic activity was due to the exceedingly dispersed Ag₂O-guar gum nanocomposite where effective separation rate of energy driven electron-hole pairs and stronger light absorption occurs. The possible mechanism of the reactions was implicated in understanding the active species involved in the photocatalytic study.

Sonication-assisted synthesis of a new heterostructured schiff base ligand Silver-Guar gum encapsulated nanocomposite as a visible light photocatalyst

A heterostructured Schiff base ligand (Benzildiethylenetriamine)-Silver-Guar gum encapsulated nanocomposites was intended to prepare by simple sonication assisted reflux method. Appropriate composition of purified guar gum, Schiff base ligand and silver nitrate were used for the synthesis. The synthesised nanocomposites were characterised by photoluminescence spectrum, UV-vis diffuse reflectance spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The crystalline peaks of XRD and FTIR reveals that Schiff base ligand and guar gum forms metal-organic matrix. Morphology studies have confirmed the organic framework structure and metallic silver nanoparticles are embedded on the organic framework. The efficiency of nanocomposites depends on adsorption capacity and silver nanoparticles that are encapsulated thereby increasing the visible light absorption through surface plasma resonance. The nanocomposite was proved to be highly selective in hydrogenation reaction which favoured the formation of aniline from nitrobenzene as single product with short reaction time and 90% conversion.

Photocatalytic and photoelectrocatalytic performance of sonochemically synthesized Cu2O@TiO2 heterojunction nanocomposites

Cu₂O@TiO₂ heterojunction nanocomposites were prepared via ultrasonic method towards the removal of the environmental pollutant of MO by the visible light photocatalytic approach. The structure of prepared Cu₂O@TiO₂ heterojunction nanocomposites was analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, photoluminescence spectroscopy, UV-Visible absorption spectroscopy, diffused reflectance spectroscopy. The photocatalytic degradation ability was tested using methyl orange as a model pollutant. From the observed pseudo-first order reaction, it was clear that Cu₂O@TiO₂ nanocomposites showed enhanced photocatalytic activity (rate = 0.223 s^-1). The formation of demethylated methyl orange as an intermediate was identified from HPLC analysis at a retention time of 3.47 min. When doped with Cu₂O, the TiO₂ preserved the integrity of its structural, revealing the morphology there is no significant changes have been made, favoring photoelectrochemical appliances. In presence of illumination, the photocurrent of Cu₂O@TiO₂ was 4.5 folds greater than that of TiO₂, involving that incorporating with Cu₂O extensively enhanced mobility of electron via reducing the recombination rate of electron-hole pairs.

A simple approach for the sonochemical synthesis of Fe3O4-guargum nanocomposite and its catalytic reduction of p-nitroaniline

In this present study, a facile and green method to synthesize highly stable Fe₃O₄-guar gum nanocomposite using ultrasound was reported. Thermal gravimetric analysis, fourier transform infrared spectroscopy, X-ray diffractometry, field emission scanning electron microscopy, energy dispersive spectroscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the crystal structure, size and morphology, elemental composition, metal-metal and metal-oxygen bonds of the synthesized nanocomposites. Fe₃O₄-guar gum nanocomposite with a size of ∼48nm was obtained as from TEM. The physicochemical characterization supports the feasibility of guar gum as an efficient stabilizing agent for the formation of nanocomposite; guar gum acts as a capping agent with a zeta potential value of -34.8 which was found to be beneficial for achieving lower particle size. Guar gum serves as a matrix for both reduction and stabilization of nanocomposite. The HR-TEM and XPS shows that Fe₃O₄ nanoparticles are encapsulated by the guar gum polymeric networks or Fe₃O₄-guar gum core-shell structure. The guar gum encapsulated magnetite nanocomposite has performed better in terms of catalytic activity for the liquid phase reduction of p-nitroaniline. The simple catalytic reduction of p-nitroaniline showed an efficiency of 47% and further exceptional improvement of up to 98% reduction within 60min with the addition of sodium borohydride was achieved. The sonochemical synthesis of Fe₃O₄-guar gum nanocomposite does not require stringent experimental conditions or any toxic agents, and thus, a straightforward, rapid, efficient and green method for the fabrication of highly active catalysts for treating environmental pollutants.

Sonochemical synthesis of porous NiTiO3 nanorods for photocatalytic degradation of ceftiofur sodium

Porous NiTiO₃ nanorods were synthesized through the sonochemical route followed by calcination at various temperature conditions. Surface morphology of the samples was tuned by varying the heat treatment temperature from 100 to 600°C. The synthesized NiTiO₃ nanorods were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, diffused reflectance spectroscopy, photoluminescence spectroscopy and Brunauer-Emmett-Teller (BET) analyses. The characterization studies revealed that the NiTiO₃ nanomaterial was tuned to porous and perfectly rod shaped structure during the heat treatment at 600°C. The porous NiTiO₃ nanorods showed visible optical response and thus can be utilized in the photocatalytic degradation of ceftiofur sodium (CFS) under direct sunlight. The photoluminescence intensity of the porous NiTiO₃ nanorods formed while heating at 600°C was lower than that of the as-synthesized NiTiO₃ sample owing to the photogenerated electrons delocalization along the one dimensional nanorods and this delocalization resulted in the reduction of the electron-hole recombination rate. The photocatalytic degradation of ceftiofur sodium (CFS) was carried out using NiTiO₃ nanorods under the direct sunlight irradiation and their intermediate products were analysed through HPLC to deduce the possible degradation mechanism. The porous NiTiO₃ nanorods exhibited an excellent photocatalytic activity towards the CFS degradation and further, the photocatalytic activity was increased by the addition of peroxomonosulfate owing to the simultaneous generation of both OH and SO₄^-.

Synthesis of Fe-doped Bi2O3 nanocatalyst and its sonophotocatalytic activity on synthetic dye and real textile wastewater

The catalysts such as Fe, Bi₂O₃, and Fe-doped Bi₂O₃ were synthesized for the sonophotocatalytic treatment of synthetic dye and real textile wastewater. The resultant catalysts were characterized for its size and uniform shape using x-ray diffractogram (XRD) and scanning electron microscopy (SEM) which signified the nanorod shape formed Bi₂O₃. The higher ultraviolet light absorbance capacity of the catalysts was also evident using diffuse reflectance spectroscopy (DRS). Initially, the effect of conventional parameters such as initial pH, gas bubbling (argon, oxygen, air and nitrogen) and oxidant addition (H₂O₂ and peroxymonosulfate) in the presence of sonolysis (22 and 37 kHz frequency) and photolysis (UV-C light) on 10 ppm Basic Brown 1 dye was studied. The results showed that highest decolorization of 62 % was attained for 3 g/L peroxymonosulfate under 37 kHz frequency sonolysis treatment. Secondly, with the catalyst study, highest of 46 % dye color removal was obtained with 4 g/L Fe under 37 kHz frequency sonolysis treatment. The sonophotocatalytic treatment of dye with Fe-doped Bi₂O₃ catalyst in combination with peroxymonosulfate showed highest color removal of 99 %. Finally, the sonophotocatalytic treatment of real textile wastewater in the presence of 3 g/L Fe-doped Bi₂O₃ and 6 g/L peroxymonosulfate reduced the total organic carbon (TOC) and chemical oxygen demand (COD) level to 77 and 91 %, respectively, in 180 min. The reported treatment process was found to treat the synthetic dye and real textile wastewater effectively.

Sonochemical synthesis of Cu2O nanocubes for enhanced chemiluminescence applications

A facile one-step sonochemical synthesis of Cu2O nanocubes has been developed by ultrasound irradiation of copper sulfate in the presence of polyvinylpyrrolidone and ascorbic acid at pH 11. During sonication, the reaction between acoustic cavitation-generated radicals and CuSO4 produced Cu(OH)2 intermediate which then reacted with ascorbic acid to generate Cu2O nanocubes. The products were characterized by FT-IR, XRD, HRTEM, AFM and particle size analyzer. The prepared Cu2O nanocubes were found to be very effective for enhancing chemiluminescence in the presence of luminol-H2O2 system.

Sonophotocatalytic treatment of Bismarck Brown G dye and real textile effluent using synthesized novel Fe(0)-doped TiO2 catalyst

Using a novel Fe(0)-TiO₂-doped catalyst, the degradation of Bismarck Brown G dye was compared by means of advanced oxidation processes, such as sonolysis, photolysis (UV light) and sonophotolysis. The sonophotolysis methodology was also adopted for real textile effluent.

Synthesis of TiO2/WO3 nanoparticles via sonochemical approach for the photocatalytic degradation of methylene blue under visible light illumination

Through an ultrasound assisted method, TiO2/WO3 nanoparticles were synthesized at room temperature. The XRD pattern of as-prepared TiO2/WO3 nanoparticles matches well with that of pure monoclinic WO3 and rutile TiO2 nanoparticles. TEM images show that the prepared TiO2/WO3 nanoparticles consist of mixed square and hexagonal shape particles about 8-12nm in diameter. The photocatalytic activity of TiO2/WO3 nanoparticles was tested for the degradation of a wastewater containing methylene blue (MB) under visible light illumination. The TiO2/WO3 nanoparticles exhibits a higher degradation rate constant (6.72×10(-4)s(-1)) than bare TiO2 nanoparticles (1.72×10(-4)s(-1)) under similar experimental conditions.

Iron-loaded mangosteen as a heterogeneous Fenton catalyst for the treatment of landfill leachate

Iron-loaded mangosteen shell powder (Fe-MSP) was found as an effective heterogeneous Fenton catalyst for the treatment of stabilized landfill leachate. Sonolytically produced catalyst has higher efficiency than other catalysts. At the optimal conditions (pH 3, catalyst concentration of 1,750 mg/L and hydrogen peroxide concentration of 0.26 M), 81 % of the chemical oxygen demand (COD) was removed effectively from the landfill leachate. But, the efficiency of Fe-MSP was reduced in the first recycling due to the poisoning of active sites. A metal leaching study indicated that the degradation of the pollutant is mainly due to solid Fe ions present in Fe-MSP rather than the leached ferrous and ferric ions. Hydroxyl radical production in the system was confirmed by the Fenton oxidation of benzoic acid. Compared to the homogeneous Fenton process, the heterogeneous Fenton process using Fe-MSP had higher COD removal efficiency, indicating the practical applicability of the prepared catalyst.

Physical insight into the sonochemical degradation of 2,4-dichlorophenol

In this study, we have attempted to reveal the physical or mechanistic features of the sonochemical degradation of 2,4-dichlorophenol (2,4-DCP). The principal physical phenomenon underlying sonochemical effects is radial motion of cavitation bubbles and production of radicals from transient collapse of these bubbles. We reveal some important physical facets of sonochemical degradation of 2,4-DCP by adopting dual approach of coupling experimental results with simulations of radial motion of cavitation bubble. First, the location of the degradation is predominantly the interfacial region between bubble and bulk medium, and secondly, the extent of degradation is controlled by conservation--and not the production--of oxidizing radicals that affects the probability of radical-pollutant interaction.

Physical facets of ultrasonic cavitational synthesis of zinc ferrite particles

This paper addresses the physical features of the ultrasonic cavitational synthesis of zinc ferrite particles and tries to establish the relationship between cavitation physics and sonochemistry of the zinc ferrite synthesis. A dual approach of coupling experimental results with simulations of radial motion of cavitation bubbles has been adopted. The precursors for the zinc ferrite, viz. ZnO and Fe(3)O(4) are produced in situ by the hydrolysis of Zn and Fe(II) acetates stimulated by (*)OH radicals produced from the transient collapse of the cavitation bubbles. Experiments performed under different conditions create significant variation in the production of (*)OH radicals, and hence, the rate of acetate hydrolysis. Correlation of the results of experiments and simulations sheds light on the important facets of the physical mechanism of ultrasonic cavitational zinc ferrite synthesis. It is revealed that too much or too little rate of acetate hydrolysis results in smaller particle size of zinc ferrite. The first effect of a higher rate of hydrolysis leads to excessively large growth of particles, due to which they become susceptible to the disruptive action of cavitation bubbles. Whereas, the second effect of too small rate of hydrolysis of Zn and Fe(II) acetates restricts the growth of particles. It has been observed that the initial reactant concentration does not influence the mean particle size or the size distribution of zinc ferrite particles. The present investigation clearly confirms that the rate-controlling step of zinc ferrite synthesis through ultrasonic cavitational route is the rate of formation of (*)OH radicals from cavitation bubbles.

Physical insights into the sonochemical degradation of recalcitrant organic pollutants with cavitation bubble dynamics

This paper tries to discern the mechanistic features of sonochemical degradation of recalcitrant organic pollutants using five model compounds, viz. phenol (Ph), chlorobenzene (CB), nitrobenzene (NB), p-nitrophenol (PNP) and 2,4-dichlorophenol (2,4-DCP). The sonochemical degradation of the pollutant can occur in three distinct pathways: hydroxylation by ()OH radicals produced from cavitation bubbles (either in the bubble-bulk interfacial region or in the bulk liquid medium), thermal decomposition in cavitation bubble and thermal decomposition at the bubble-liquid interfacial region. With the methodology of coupling experiments under different conditions (which alter the nature of the cavitation phenomena in the bulk liquid medium) with the simulations of radial motion of cavitation bubbles, we have tried to discern the relative contribution of each of the above pathway to overall degradation of the pollutant. Moreover, we have also tried to correlate the predominant degradation mechanism to the physico-chemical properties of the pollutant. The contribution of secondary factors such as probability of radical-pollutant interaction and extent of radical scavenging (or conservation) in the medium has also been identified. Simultaneous analysis of the trends in degradation with different experimental techniques and simulation results reveals interesting mechanistic features of sonochemical degradation of the model pollutants. The physical properties that determine the predominant degradation pathway are vapor pressure, solubility and hydrophobicity. Degradation of Ph occurs mainly by hydroxylation in bulk medium; degradation of CB occurs via thermal decomposition inside the bubble, degradation of PNP occurs via pyrolytic decomposition at bubble interface, while hydroxylation at bubble interface contributes to degradation of NB and 2,4-DCP.

Physical features of sonochemical degradation of nitroaromatic pollutants

This article attempts to discern the physical (or mechanistic) features of the sonochemical degradation of two major and ubiquitous nitroaromatic pollutants, viz. nitrobenzene and p-nitrophenol. The fundamental physical phenomenon behind sonochemical degradation of pollutants is radial motion of cavitation bubbles. This study implements a dual approach to the problem, i.e. results of the experiments under different conditions have been coupled to a mathematical model that addresses physics and chemistry of the cavitation bubbles. Various experimental techniques applied in this study influence important physical parameters related to cavitation phenomenon in the liquid medium such as extent of radical production from the bubble, thickness of the liquid shell surrounding the bubble that gets heated up during transient collapse, the concentration of the pollutant in the interfacial region and extent of radical scavenging in the medium. Concurrent analysis of the experimental and simulation results reveal that overall degradation of the pollutant achieved for a given combination of experimental conditions is a function of competing (and sometimes conflicting) effect of these parameters. A semi-quantitative account of the relative influence of these parameters and the interrelations between them is presented.