Synthesis of magnetic γ-Fe2O3-based nanomaterial for ultrasonic assisted dyes adsorption: Modeling and optimization

γ-Fe₂O₃ nanoparticles were synthesized and loaded on activated carbon. The prepared nanomaterial was characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transforms infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The γ-Fe₂O₃ nanoparticle-loaded activated carbon (γ-Fe₂O₃-NPs-AC) was used as novel adsorbent for the ultrasonic-assisted removal of methylene blue (MB) and malachite green (MG). Response surface methodology and artificial neural network were applied to model and optimize the adsorption of the MB and MG in their individual and binary solutions followed by the investigation on adsorption isotherm and kinetics. The individual effects of parameters such as pH, mass of adsorbent, ultrasonication time as well as MB and MG concentrations in addition to the effects of their possible interactions on the adsorption process were investigated. The numerical optimization revealed that the optimum adsorption (>99.5% for each dye) is obtained at 0.02 g, 15 mg L⁻¹, 4 min and 7.0 corresponding to the adsorbent mass, each dye concentration, sonication time and pH, respectively. The Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherms were studied. The Langmuir was found to be most applicable isotherm which predicted maximum monolayer adsorption capacities of 195.55 and 207.04 mg g⁻¹ for the adsorption of MB and MG, respectively. The pseudo-second order model was found to be applicable for the adsorption kinetics. Blank experiments (without any adsorbent) were run to investigate the possible degradation of the dyes studied in presence of ultrasonication. No dyes degradation was observed.     

Targeted sonocatalytic cancer cell injury using avidin-conjugated titanium dioxide nanoparticles

In this study, we applied sonodynamic therapy to cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with avidin protein, which preferentially discriminated cancerous cells from healthy cells. Subsequently, hydroxyl radicals were generated from the TiO₂ NPs after activation by external ultrasound irradiation (TiO₂/US treatment). Although 30% of the normal breast cells (human mammary epithelial cells) exhibited the uptake of avidin-modified TiO₂ NPs, over 80% of the breast cancer cells (MCF-7) exhibited the uptake of avidin-TiO₂ NPs. Next the effect of the TiO₂/US treatment on MCF-7 cell growth was examined for up to 96 h after 1-MHz ultrasound was applied (0.1 W/cm², 30 s) to cells that incorporated the TiO₂ NPs. No apparent cell injury was observed until 24 h after the treatment, but the viable cell concentration declined to 68% compared with the control at 96 h.     

A comparative DFT study of adsorption and catalytic performance of Au nanoparticles at anatase and brookite TiO2 surfaces

We have compared the adsorption properties of small Au_n (n = 1–8) nanoparticles on the defect-free (stoichiometric) and defective (partially reduced) brookite TiO₂(210) and anatase TiO₂(101) surfaces using density functional theory calculations. The interaction between Au atoms and anatase TiO₂(101) was determined to be quite weak and small Au_n particles grown at defects (O vacancies) prefer extended 2D structures. By contrast, dispersion and 3D configurations appear to be favored at brookite TiO₂(210) for Au_n nanoparticles due to their strong interaction. Calculations of CO oxidation at Au_n (n = 6–8) particles supported at defective brookite TiO₂(210) show that occurrence of protruding low-coordinated Au atoms is essential for favorable CO adsorption and subsequent reaction with O₂. In particular, the configuration of the Au_n nanoparticles can determine the energetics in the formation of active Au atoms, and their mobility also affects the reaction between CO and O₂ (or O).     

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 8–12 nm 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.     

Ultrasound-assisted adsorption of copper(II) ions on hazelnut shell activated carbon

The present study was aimed to removal of Cu(II) ions from aqueous solution by ultrasound-assisted adsorption onto the granular activated carbon obtained from hazelnut shells. The attention was focused on modeling the equilibrium and kinetics of Cu(II) adsorption onto the granular activated carbon. The granular activated carbon was prepared from ground dried hazelnut shells by simultaneous carbonization and activation by water steam at 950 °C for 2 h. Adsorption isotherm data were better fitted by the Langmuir model than the Freundlich model in both the absence and the presence of ultrasound. The maximum adsorption capacity of the adsorbent for Cu(II), calculated from the Langmuir isotherms, in the presence of ultrasound (3.77 mmol/g) is greater than that in the absence of ultrasound (3.14 mmol/g). The adsorption process in the absence and the presence of ultrasound obeyed to the pseudo second-order kinetics. The removal of Cu(II) ions was higher in the presence of ultrasound than in its absence, but ultrasound reduced the rate constant. The intraparticular diffusion model indicated that adsorption of Cu(II) ions on the granular activated carbon was diffusion controlled as well as that ultrasound promoted intraparticular diffusion.     

Enhanced efficiency of dye-sensitized solar cells by UV–O3 treatment of TiO2 layer

Solar conversion efficiency of dye-sensitized solar cells was improved by UV–O₃ treatment of TiO₂ before and/or after sintering. The enhancement was resulted from the removal of the residual organics originated from the TiO₂ precursor pastes, increased adsorption of dyes to the TiO₂, surface, and longer diffusion length and shorter electron transit time of electrons through the TiO₂ mesoscopic structure. The power conversion efficiency of the cells reaches to 7.2% with the open circuit voltage of 0.71 V, the short circuit current density of 15.2 mA/cm² and the fill factor of 0.67 under illumination with AM 1.5 (100 mW/cm²) simulated sunlight.     

Facile strategy for stability control of gold nanoparticles synthesized by aqueous reduction method

A facile strategy for controlling sizes and stabilities of gold nanoparticles synthesized by aqueous reduction method was experimentally examined and reported. When pH of the solution of HAuCl₄ and Na₃C₆H₅O₇ was controlled by introducing either NaOH or HCl with different concentration, the zeta potential of suspension of gold nanoparticles changed accordingly. With the strategy using a control of pH in a range of 5–9, the zeta potential of synthesized gold nanoparticles was regulated in a range of −60 to −40 mV, resulting in a stable red suspension of gold nanoparticles. Under a condition with pH < 5.0, gold nanoparticles could agglomerate after being kept quiescently for a day due to an adsorption of H⁺ on their surface, which in turn enhanced the attractive van der Waals interaction. On the other hand, synthesis of gold nanoparticles with pH > 9.1 would provide a lower amount of gold nanoparticles due to the formation of NaAuO₂. Based on these results, a potential mechanism of gold nanoparticle synthesis was also discussed.     

Acute effects of sono-activated photocatalytic titanium dioxide nanoparticles on oral squamous cell carcinoma

Sonodynamic therapy (SDT) is a new treatment modality using ultrasound to activate certain chemical sensitizers for cancer therapy. In this study, effects of high intensity focused ultrasound (HIFU) combined with photocatalytic titanium dioxide (TiO₂) nanoparticles on human oral squamous cell line HSC-2 were investigated. Viability of HSC-2 cells after 0, 0.1, 1, or 3 s of HIFU irradiation with 20, 32, 55 and 73 W cm⁻² intensities in the presence or absence of TiO₂ was measured immediately after the exposures in vitro. Immediate effects of HIFU (3 s, 73 W cm⁻²) combined with TiO₂ on solid tumors were also examined by histological study. Cytotoxic effect of HIFU + TiO₂ in vitro was significantly higher than that of TiO₂ or HIFU alone with the tendency to increase for higher HIFU intensity, duration, and TiO₂ concentration in the suspension. In vivo results showed significant necrosis and tissue damage in HIFU and HIFU + TiO₂ treated samples. However, penetration of TiO₂ nanoparticles into the cell cytoplasm was only observed in HIFU + TiO₂ treated tissues. In this study, our findings provide a rational basis for the development of an effective HIFU based sonodynamic activation method. This approach offers an attractive non-invasive therapy technique for oral cancer in future.     

Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO2(110): An STM and TPD study

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O₂ with reduced TiO₂(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O₂ dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O₂ dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O₂ dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O₂ interaction channels and the TPD data, a new comprehensive model of the O₂ chemisorption on reduced TiO₂(110) is proposed. The model explains the relations between the two dissociative and the molecular O₂ interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO₂(110) crystals, the kinetics of the two O₂ dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.     

Enhanced photocatalytic–electrolytic degradation of Reactive Brilliant Red X-3B in the presence of water jet cavitation

Photocatalysis, electrolysis, water jet cavitation (WJC), alone and in combinations were applied to degrade an azo dye, Reactive Brilliant Red X-3B (X-3B). Experiments were conducted in a 4.0 L aqueous solution with different initial dye concentrations, TiO₂ dose, and solution pH. WJC substantially increased the photocatalytic, electrolytic and photocatalytic–electrolytic rates of the dye removal. The observed first-order rate of X-3B decolorization in the process of combined photocatalysis and electrolysis coupled with WJC was 1.6–2.9 times of that in the process of combined photocatalysis and electrolysis coupled with mechanical stirring. The rate enhancements may be attributed primarily to the reduced diffusion layer thickness on the electrodes and the deagglomeration of photocatalyst particles due to the chemical and physical effects of WJC. Under the conditions of 80 mg/L X-3B solution, 100 mg/L TiO₂ dose and solution pH 6.3, 97% and 71% of color and chemical oxygen demand (COD_Cr) were removed, respectively, within 90-min photocatalytic–electrolytic treatment coupled with WJC. During this process, azo groups and naphthalene, benzene and triazine structures of the dye can be destroyed. Industrial textile effluent was also investigated, and a positive synergistic effect between photocatalytic–electrolytic system and WJC was observed considering color removal.     

Ultrasound-assisted adsorption of 4-dodecylbenzene sulfonate from aqueous solutions by corn cob activated carbon

This study was aimed at removal of 4-dodecylbenzene sulfonate (DBS) ions from aqueous solutions by ultrasound-assisted adsorption onto the carbonized corn cob (AC). The main attention was focused on modeling the equilibrium and kinetics of adsorption of DBS onto the AC. The AC was prepared from ground dried corn cob by carbonization and activation by carbon dioxide at 880 °C for 2 h in a rotary furnace. The adsorption isotherm data were fitted by the Langmuir model in both the absence and the presence of ultrasound (US). The maximum adsorption capacities of the adsorbent for DBS, calculated from the Langmuir isotherms, were 29.41 mg/g and 27.78 mg/g in the presence of US and its absence, respectively. The adsorption process in the absence and the presence of US obeyed the pseudo second-order kinetics. The intraparticular diffusion model indicated that the adsorption of DBS ions on the AC was diffusion controlled as well as that US promoted intraparticular diffusion. The ΔG° values, ?24.03 kJ/mol, ?25.78 kJ/mol and ?27.78 kJ/mol, were negative at all operating temperatures, verifying that the adsorption of DBS ions was spontaneous and thermodynamically favorable. The positive value of ΔS° = 187 J/mol K indicated the increased randomness at the adsorbent–adsorbate interface during the adsorption of DBS ions by the AC.     

Adsorption of γ-mercaptopropyltrimethoxysilane on zinc: A study of the competition between thiol and silanol functions related to the age of the siloxane solution,its pH and the oxidation state of the surface

We describe the adsorption of γ–mercaptopropyltrimethoxysilane (γ-MPS) on zinc under various experimental conditions, including the age of the siloxane solution (t_ag), its pH (7 or 4), and the mode of preparation of the surface (RCA treatment or in situ polishing). It is shown by XPS studies that the structure of the adsorbed monolayer varies dramatically with the pH of the solution. At the natural pH of the siloxane solution (pH 7) where no hydrolysis of the SiOCH₃ group occurs, adsorption proceeds through the SH moiety and not through SiOCH₃ groups. This preferential attachment through SH is found whatever the age of the solution and the treatment of the zinc. It is confirmed by the fact that n-propyltrimethoxysilane (PSi) does not interact with the surface in the case of very old solutions (adsorption is not observed when Zn is polished in situ and only occurs with RCA zinc treatment for t_ag > 40 min). With siloxane solutions at pH 4, adsorption of γ-MPS is more complex and the structure of the adsorbed layer depends mainly on the age of the solution. With a fresh solution, hydrolysis is not very advanced and, as mentioned previously, adsorption occurs through the SH group. With older solutions and as a consequence of the progressive hydrolysis of the SiOCH₃ group to SiOH, the density of the grafted siloxane monolayer increases (6 min < t_ag < 10 min), followed by a mixed adsorption through SH and SiOH (10 min < t_ag < 40–50 min) revealed by the decrease in the normalised (Si2p/S2p)* intensity ratio. Finally, adsorption of dimers and oligomers is observed with still older siloxane solutions. In contrast to PSi whose adsorption on zinc is favoured by the RCA treatment, neither treatment of the surface changes the results significantly in the case of γ-MPS. Comparison with alkanethiols confirms the transition from monomer to dimer adsorption and IRRAS studies clearly indicate a condensation reaction between OH and SH groups.     

Highly efficient simultaneous ultrasonic-assisted adsorption of Pb(II), Cd(II), Ni(II) and Cu (II) ions from aqueous solutions by graphene oxide modified with 2,2′-dipyridylamine: Central composite design optimization

In present work, a graphene oxide chemically modified with 2,2′-dipyridylamine (GO-DPA), was synthesized by simple, fast and low-cost process for the simultaneous adsorption of four toxic heavy metals, Pb(II), Cd(II), Ni(II) and Cu(II), from aqueous solutions. The synthesized adsorbent was characterized by FT-IR, XRD, XPS, SEM and AFM measurements. The effects of variables such as pH solution, initial ion concentrations, adsorbent dosage and sonicating time were investigated on adsorption efficiency by rotatable central composite design. The optimum conditions, specified as 8 mg of adsorbent, 20 mg L⁻¹ of each ion at pH 5 and short time of 4 min led to the achievement of a high adsorption capacities. Ultrasonic power had important role in shortening the adsorption time of ions by enhancing the dispersion of adsorbent in solution. The adsorption kinetic studies and equilibrium isotherms for evaluating the mechanism of adsorption process showed a good fit to the pseudo-second order and Langmuir model, respectively. The maximum adsorption capacities (Q_m) of this adsorbent were 369.749, 257.201, 180.893 and 358.824 mg g⁻¹ for lead, cadmium, nickel and copper ions, respectively. The removal performance of adsorbent on the real wastewater samples also showed the feasibility of adsorbent for applying in industrial purposes.     

Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process

This paper aims to study fabrication and characterization of silver/titanium oxide composite nanoparticle through sonochemical process in the presence of ethylene glycol with alkaline solution. By using ultrasonic irradiation of a mixture of silver nitrate, the dispersed TiO₂ nanoparticle in ethylene glycol associated with aqueous solution of sodium oxide yields Ag/TiO₂ composite nanoparticle with shell/core-type geometry. The powder X-ray diffraction (XRD) of the Ag/TiO₂ composites showed additional diffraction peaks corresponding to the face-centered cubic (fcc) structure of silver crystallization phase, apart from the signals from the cores of TiO₂. Transmission electron microscopy (TEM) images of Ag/TiO₂ composites, which average particle size is roughly 80 nm, reveal that the titanium oxide coated by Ag nanoparticle with a grain size of about 2–5 nm. Additionally, the formation of silver nanoparticles on TiO₂ was monitored by ultraviolet visible light spectrophotometer (UV–Vis). As measured the optical absorption spectra of as-synthesized Ag nanoparticle varying with time, the mechanism of surface formatting silver shell on the cores of TiO₂ could be explored by autocatalytic reaction; the conversion of Ag particle from silver ion is 98% for the reaction time of 1000 s; and the activity energy of synthesizing Ag nanoparticles on TiO₂ is 40 kJ/mol at temperature ranging from 5 to 25 °C. Hopefully, this preliminary investigation could be used for mass production of composite nanoparticles assisted by ultrasonic chemistry in the future.     

Hydrothermal synthesis of TiO2 nanocrystals in different basic pHs and their applications in dye sensitized solar cells

In this research TiO₂ nanocrystals with sizes about 11–70 nm were grown by hydrothermal method. The process was performed in basic autoclaving pH in the range of 8.0–12.0. The synthesized anatase phase TiO₂ nanocrystals were then applied in the phtoanode of the dye sensitized solar cells. It was shown that the final average size of the nanocrystals was larger when the growth was carried out in higher autoclaving pHs. The photoanodes made of TiO₂ nanocrystals prepared in the pHs of 8.0 and 9.0 represented low amounts of dye adsorption and light scattering. The performance of the corresponding dye sensitized solar cells was also not acceptable. Nevertheless, the energy conversion efficiency was better for the state of pH of 9.0. For the photoanodes made of TiO₂ nanocrystals prepared at autoclaving pH of 10.0, the dye adsorption and light scattering were quite higher. The photovoltaic characteristics of the best cell in this state were 15.25 mA/cm², 740 mV, 0.6 and 6.8% for the short-circuit current density, open-circuit voltage, fill factor and efficiency, respectively. The photoanodes composed of TiO₂ nanocrystals prepared in autoclaving pHs of 11.0 and 12.0 demonstrated lower amount of dye adsorption and higher light scattering. This was quite considerable for the state of pH of 12.0. The energy conversion efficiencies were consequently decreased compared to that of the pH of 10.0. The optimum situation was finally discussed based on the nanocrystals size and its influence on the sensitization and light harvesting efficiency.     

Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis

Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2–4 bar) and initial pH of the solution (4–7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO₂ and H₂O₂ have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO₂ and UV/TiO₂/H₂O₂ results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO₂/H₂O₂ under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis.     

A corrosion-resistance superhydrophobic TiO2 film

A superhydrophobic TiO₂ film with water contact angle greater than 170° on Hastelloy substrate was fabricated through simply dip-coating method from TiO₂ precursor solution containing TiO₂ nanoparticles with the average diameter 25 nm, followed by heat-treatment and modification with fluoroalkylsilane (FAS) molecules. The as-obtained sample was characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and water contact angle measurement respectively. Moreover, the dynamic light scattering (DLS) size distribution of TiO₂ aggregated particles in the TiO₂ precursor solution containing P25 particles was evaluated by Laser Particle Sizer. It is found that the TiO₂ nanoparticles in TiO₂ precursor solution play a crucial role to form high superhydrophobicity. Simultaneously, the superhydrophobic TiO₂ film still showed great superhydrophobicity after corroded with strong acid or alkali solutions and protected the substrate from corrosion which should be critical to the potential application in industry.     

Stability of gold nanostructures on rutile TiO2(110) surface

The adsorption of gold atoms and formation of nanostructures on the rutile TiO₂(110) surface with different degree of oxygen reduction was studied from first principles. The Au atoms adsorb strongest at oxygen vacancy sites. Starting from a very low coverage limit the potential energy profiles or diffusion paths of the adsorbed Au monomers and dimers were calculated. Stable structures of two to nine Au atoms arranged in finite and infinite rows and in the shape of finite-size clusters were determined. All these structures are found to bind to the reduced surface stronger than 2 eV/atom. The elongated Au row-like structures bind by about 0.1 eV stronger than 3D clusters, suggesting a preference for the 1D-like Au growth mode on the missing-row reconstructed TiO₂(110).     

Preparation and photocatalytic activity of bicrystal phase TiO2 nanotubes containing TiO2-B and anatase

Bicrystal phase TiO₂ nanotubes (NTS) containing monoclinic TiO₂-B and anatase were prepared by the hydrothermal reaction of anatase nanoparticles with NaOH aqueous solution and a heat treatment. Their structure was characterized by XRD, TEM and Raman spectra. The results showed that the bicrystal phase TiO₂ NTS were formed after calcining H₂Ti₄O₉·H₂O NTS at 573 K. The bicrystal phase TiO₂ NTS exhibit significantly higher photocatalytic activity than the single phase anatase NTS and Dessuga P-25 nanoparticles in the degradation of Methyl Orange aqueous solution under ultraviolet light irradiation, which is attributed to the large surface and interface areas of the bicrystal phase TiO₂ NTS.     

Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO₂ nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10 wt%) were prepared by a sol–gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1 eV. Photocatalytic results indicated that TiO₂ had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO₂ nanoparticles. Among the samples, Fe-1 wt% doped TiO₂ nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.