Adsorption of Textile Dye on Zinc Stannate Oxide: Equilibrium,Kinetic and Thermodynamics Studies

Zn₂SnO₄ powder was prepared by hydrothermal process at 200°C for 12 h. The material was characterized by X-ray-diffraction and surface area. The synthesized sample presented a pure phase and a surface area of 48.8 m² · g^?1. It was used as adsorbent to remove the Reactive Red 141 that is a azo textile dye. The adsorption kinetics of the textile dye on Zn₂SnO₄ followed the pseudo-second-order model. The adsorption process was found to be controlled by both external mass transfer and intraparticle diffusion. The equilibrium data were in good agreement with both Langmuir and Freundlich isotherms. Thermodynamic parameters were calculated, and the results revealed that the adsorption process is endothermic in nature, with weak forces of the Van der Walls acting.     

Synthesis of High Surface Area MgAl2O4 Nanopowder as Adsorbent for Leather Dye Removal

Abstract

MgAl₂O₄ nanopowder has been prepared by alkoxides hydrolysis with further calcination at temperature of 700°C. The adsorption of a leather dye, Direct Black 38, onto this material was investigated. The sample was characterized by X-ray-diffraction (XRD), N₂ adsorption–desorption isotherm and Fourier transform infrared spectroscopy. The results showed that sample present a pure phase, and the average nanocrystal size of 8 nm, the BET surface area is about 206.5 m² · g^?1 and total pore volume is about 1.44 cm³ · g^?1. Adsorption kinetics data were modeled by film and pore diffusion model. The experimental isotherm was described by the Langmuir model. MgAl₂O₄ nanopowder presented a great removal efficiency of leather dye by adsorption process, with a maximum adsorption capacity of 833 mg of dye per gram of adsorbent.     

Surfactant-free microwave hydrothermal synthesis of SnO2 nanosheets as an anode material for lithium battery applications

SnO₂ nanosheets were synthesized using microwave hydrothermal method without using a surfactant and organic solvents. Formation of pure nanocrystalline rutile phase of SnO₂ sample was confirmed by X-ray diffraction (XRD) results and the average crystallite size of SnO₂ sample calculated using Scherrer's formula and XRD data is found to be 6 nm. HR-TEM, SAED and EDX results showed the formation of agglomerated nanosize sheets like morphology with high porous structured SnO₂ powder. Further, the formation of high porous structured SnO₂ powder was confirmed from BET surface area results (59.28 m² g^?1). The electrochemical performance of the lithium-ion battery made up of SnO₂ nanosheets, as an anode, was tested through the cyclic voltammetry and galvanostatic charge-discharge measurements. The galvanostatic charge-discharge results of the lithium-ion battery showed good discharge capacity of 257.8 mAh g^?1 after 50 cycles at a current density of 100 mA g^?1. The improved electrochemical properties may be due to the formation of a unique nanosize sheets type morphology with high porous structured SnO₂ powder. High porous structured nanosize sheets type morphology of SnO₂ can help to reduce the diffusion length and sustain the volume changes during the charging-discharging process.Hence, high porous structured nanosize sheets morphology of SnO₂ prepared using the microwave hydrothermal method without using a surfactant and organic solvents can be a better anode material for lithium ion battery applications.     

Effects of anions on the photocatalytic and photoelectrocatalytic degradation of reactive dye in a packed‐bed reactor

The effects of various anions, Cl^?, ClO₄^?, SO₄^2?, NO₃^?, HCO₃^?, H₂PO₄^? and C₂O₄^2?, on the photocatalytic and photoelectrocatalytic degradation of reactive Brilliant Orange K‐R have been investigated in a packed‐bed photoelectrocatalytic reactor. It was found that the nature and concentrations of these inorganic anions significantly affected the photocatalytic and photoelectrocatalytic degradation performance of the reactive dye. The results indicated that the external electric field was successfully applied to improve the photocatalytic efficiency of reactive Brilliant Orange K‐R in the presence of Cl^?, especially at higher concentrations, while other inorganic anions displayed more or less negative effects on the degradation of the dye. The strongest inhibition effect on photocatalytic and photoelectrocatalytic degradation of the dye was observed in the presence of HCO₃^? ions. Copyright © 2004 Society of Chemical Industry     

Water purification using a BiVO4/graphene oxide multifunctional hydrogel based on interfacial adsorption-enrichment and photocatalytic antibacterial activity

Photocatalytic degradation by visible light-driven generation of reactive oxygen species shows great promise for purification of environmental water. However, such degradation is limited by the low separation efficiency of photogenerated carriers and the poor adsorption capacity of the photocatalyst itself. To solve these problems, we successfully constructed and prepared a composite hydrogel (BV-GH) combining a three-dimensional network structure composed of graphene oxide and BiVO₄ to achieve the synergistic effects of adsorption enrichment and photocatalytic degradation. The results show that the amount of methylene blue and methyl orange adsorbed by BV-GH is 258.78 mg g^?1 and 217.16 mg g^?1, respectively, which is much higher than that obtained for pure BiVO₄. Due to the synergistic effect of adsorption enrichment and photocatalytic degradation, the degradation rate of the dye by BV-GH reaches 94.18% in 60 min, which is 6.98 times higher than that obtained for pure BiVO₄. Electron spin-resonance (ESR) experiments confirm that the main factor affecting the dye degradation by BV-GH is the ability to produce more ·OH and ·O₂^?, which is an important reason for the excellent antibacterial performance of BV-GH against E. coli. This work can provide further inspiration for photocatalytic technology in water purification.     

Boosting the photovoltaic performance of Zn2SnO4‐based dye‐sensitized solar cells by Si doping into Zn2SnO4

In the present work, Zn₂SnO₄ nanoparticles were doped with silicon to improve their electrical and optical properties by the conventional solid‐state reaction method. The results showed that the minimum electrical resistivity of about 0.09 Ωcm was obtained for Zn₂SnO₄ nanoparticles with 3% Si doping. The decrease in the electrical resistivity can be attributed to the insertion of Si⁺⁴ atoms into the Zn⁺² and/or Sn⁺⁴ sites and also the formation of more oxygen vacancies in the Zn₂SnO₄ lattice. The formation of the more oxygen vacancy defect states in Si‐doped Zn₂SnO₄ nanoparticles was verified by photoluminescence spectroscopy. The efficiency of a dye‐sensitized solar cell based on 3% Si‐doped Zn₂SnO₄ was significantly better, by about 81%, compared to that of a cell based on the undoped Zn₂SnO₄. The enhancement in the efficiency can be ascribed to the facilitation of electron transport throughout a photoelectrode due to increase in the charge carrier concentration which was caused by Si doping.     

Methylene Blue Adsorption on Natural and Modified Clays

Toxic methylene blue dye is removed from water by accumulating it on the surface of clay minerals. Clay adsorbents are obtained from kaolinite, montmorillonite, and their acid activated forms. The adsorption experiments are carried out in a batch process in environments of different pH, initial dye concentration, amount of clay, interaction time, and temperature. Adsorption of dye is best described by second order kinetics. In the temperature range of 303 to 333 K, the Langmuir monolayer capacity for three kaolinite species increased from 45.5 to 56.5 mg g^?1, 45.9 to 57.8 mg g^?1, 46.3 to 58.8 mg g^?1, and for three montmorillonites species from 163.9 to 181.8 mg g^?1, 166.7 to 188.8 mg g^?1, and 172.4 to 192.3 mg g^?1. The interaction is an endothermic process driven by entropy increase and spontaneous adsorptive accumulation is ensured by favorable Gibbs energy decrease. It is found that acid activation enhances the adsorption capacity of kaolinite and montmorillonite.     

Unexpected Photocatalytic Activity of Simple and Platinum Modified Tubular SiO2 for the Oxidation of Oxalic Acid to CO2

The photocatalytic mineralization of oxalic acid over SiO₂-based materials was investigated in the 200–800 nm range. The photocatalytic activity was found to be strongly related to the morphology of SiO₂ materials. The simple as well as the Pt-modified SiO₂ particles having a predominant spherical shape exhibited null photocatalytic activity. In contrast, the tubular shaped SiO₂ particles revealed an interesting photocatalytic activity, the rate of CO₂ evolvement being 45 µmol g _cat ^?1  h^?1. The initial activity was significantly enhanced (428 µmol CO₂ g _cat ^?1  h^?1) by platinum photodeposition on the outer and inner surface of tubular SiO₂. The catalytic materials were characterized by TEM, UV–VIS and XPS to obtain rational explanations for the phocatalytic activity that was noticed. The experiments revealed that SiO₂ tubes behave as efficient photooxidation microreactors. The morphology-dependent photocatalysis can be an efficient tool in future for the abatement of pollutants in liquid phase.     

Synthesis,characterization and enhanced visible-light photocatalytic activity of Zn2SnO4/C nanocomposites with truncated octahedron morphology

Novel Zn₂SnO₄/C nanocomposites with truncated octahedron morphology were constructed using a two-step hydrothermal synthesis route combined with subsequent calcination. The as-prepared samples were characterized by X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR), Raman spectroscopy, field–emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflection spectroscopy, photoluminescence spectroscopy (PL), and Brunauer–Emmett–Teller surface area measurements. The result of FESEM showed that the as-prepared Zn₂SnO₄/C nanocomposites are composed of numerous uniform nanoparticles with regular truncated octahedron morphology. Raman spectral characterization combined with HRTEM result revealed that a thin layer of carbon was attached on the surface of Zn₂SnO₄. Using rhodamine B (RhB) as a model organic pollutant, the visible-light photocatalytic activities of the as-prepared samples were investigated, and the photocatalytic mechanism was discussed. Compared with pure Zn₂SnO₄, Zn₂SnO₄/C nanocomposites exhibited much better visible-light photocatalytic activity. The increase in the photocatalytic activity of Zn₂SnO₄/C nanocomposites was mainly attributed to the enhancement of the optical absorption capability and efficient separation of photogenerated electron-hole pairs.     

Adsorption of different dyes from aqueous solution using Si-MCM-41 having very high surface area

Adsorption characteristics of four different dyes Safranin O (cationic), Neutral Red (neutral), Congo Red (anionic) and Reactive Red 2 (anionic) on Si-MCM-41 material having very high surface area are reported. The surface morphology of Si-MCM-41 material before and after adsorbing dye molecules are characterised by FTIR, HRXRD, nitrogen adsorption–desorption isotherms, FESEM, and HRTEM. The adsorption capacities of Si-MCM-41 for the dyes followed a decreasing order of NR > SF > CR > RR2. The adsorption kinetics, isotherm and thermodynamic parameters are investigated in detail for these dyes using calcined Si-MCM-41. The kinetics and isotherm data showed that both SF and NR adsorb more rapidly than CR and RR2, in accordance with pseudo-second-order kinetics model as well as intraparticle diffusion kinetics model and Langmuir adsorption isotherm model respectively. The thermodynamic data suggest that the dye uptake process is spontaneous. The high adsorption capacities of dyes on Si-MCM-41 (q_m = 275.5 mg g^?1 for SF, q_m = 288.2 mg g^?1 for NR) is explained on the basis of electrostatic interactions as well as H-bonding interactions between adsorbent and adsorbate molecules. Good regeneration capacity is another important aspect of the material that makes it potent for the uptake of dyes from aqueous solution.     

Synthesis and application of amine functionalized silica mesoporous magnetite nanoparticles for removal of chromium(VI) from aqueous solutions

In this research, novel nanoparticles of Kit-6 mesoporous silica magnetite were synthesized with 9.6 nm pore diameter and 241.68 m² g^?1 surface area. The synthesized mesoporous magnetite nanoparticles (MMNPs) were functionalized with amine groups. Scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption method confirmed the morphology and structure of the synthesized nanoparticles. The amine functionalized MMNPs were used for sorption of toxic chromate ions from aqueous samples. The effect of various experimental parameters (four factors at three levels) on the sorption efficiency of Cr(VI) was studied and optimized via Taguchi L₉ (3⁴) orthogonal array experimental design. At optimum conditions, the sorption of the Cr(VI) was best described by a pseudo second-order kinetic model with R² = 0.9999 and q_eq = 129.8 mg g^?1, suggesting chemisorption mechanism. Adsorption data were fitted well to the Langmuir isotherm and the synthesized sorbent showed complete ion removal with 185.2 mg g^?1sorption capacity.     

Hydrothermal synthesis of flower-like Zn2SnO4 composites and their performance as anode materials for lithium-ion batteries

Flower-like Zn₂SnO₄ composites had been prepared through a green hydrothermal synthesis. The structural, morphological and electrochemical properties were investigated by means of XRD, BET, SEM, TEM, and electrochemical measurement. The results show that the as-prepared sample is in high purity phase and of good crystallinity; meanwhile it has a particular 3-D structure and large surface area. Electrochemical measurement suggests that flower-like Zn₂SnO₄ composites exhibit better cycling properties and lower initial irreversible capacities than the solid Zn₂SnO₄ cubes. The first discharge and charge capacities of the material are 1750 mA h g⁻¹ and 880 mA h g⁻¹ respectively. A higher reversible capacity of 501 mA h g⁻¹ was obtained after 50 cycles at a current density of 300 mA g⁻¹. The higher reversible capacity and good stability can be related to the special nanostructural features of the material. Such Zn₂SnO₄ structures synthesized by the simple and cheap method are expected to have potential application in energy storage.     

Solvent free mechanochemical synthesis of MnO2 for the efficient degradation of Rhodamine-B

MnO₂ nanorods were synthesized by mechanochemical processing with subsequent heat treatment and their photocatalytic activity was studied on the decolourization of aqueous solution of Rhodamine B at different pH levels. A solid state redox reaction 2KMnO₄ + MnCl₂ → 3MnO₂ + 2KCl + O₂ was activated during mechanical milling. Excess KCl salt was added in the starting powder mixture to prevent agglomeration of MnO₂ nanoparticles. The milling resulted in the production of amorphous MnO₂ nanoparticles with a high surface area of 204 m² g^?1. Crystalline MnO₂ nanorods of diameters about 15–20 nm were produced by heating the as-milled powder at 350 °C for 1 h in air. Amorphous MnO₂ nanoparticles showed higher degradation rate of Rhodamine B than crystalline MnO₂ nanorods under simulated sunlight. The degradation rate was higher under acidic conditions. This work demonstrates the potential for cost effective, green and scalable synthesis of MnO₂ nano-catalysts for environmental applications.     

Microwave-assisted green synthesis of hybrid nanocomposite: removal of Malachite green from waste water

Gum xanthan/psyllium-based nanocomposite was prepared by microwave-assisted synthetic method for the removal of toxic Malachite green (MG) dye from aqueous solutions. The nanocomposite was prepared by in situ incorporation of the K₂Zn₃[Fe(CN)₆]·9H₂O nanoparticles into the semi-IPN matrix in the presence of ammonium persulphate and glutaraldehyde as initiator-crosslinker system. Liquid uptake efficacy of the hybrid superabsorbent was enhanced through the optimization of different reaction conditions, including APS = 0.027 mol L^?1; glutaraldehyde = 0.053 × 10^?3 mol L^?1; solvent = 8.0 mL; acrylic acid = 10.928 mol L^?1; pH 7.0; reaction time = 60 s and microwave power = 100 % and its thermal behavior was evaluated using TGA-DTG-DTA technique. Candidate nanocomposite was characterized by FTIR, SEM, XRD and UV–visible spectroscopic methods. Various optimized parameters for the efficient removal (83 %) of the Malachite green were adsorbent dose of 800 mg, 14 mg L^?1 initial dye concentration and contact time of 28 h. Further, Langmuir and Freundlich adsorption isotherms showed good applicability in adsorption process of MG onto the nanocomposite with maximum adsorption efficiency of 3.21 mg g^?1. However, for Freundlich isotherm, R ² was around 0.9947 and value of 1/n was less than 1 for the synthesized nanocomposite which indicated that the Freundlich isotherm was more favorable than Langmuir isotherm model along with its usability for wide range of dye concentrations. The nanocomposite was found to be a potential product for dye removal from waste water and could prove to be a boon for textile sector.     

Zn-doped SnO2 hierarchical structures formed by a hydrothermal route with remarkably enhanced photocatalytic performance

Zn-doped SnO₂ hierarchical structures were synthesized by a facile and low-cost hydrothermal route using tin chloride and zinc nitrate as inorganic sources. The Zn-doped SnO₂ hierarchical structures were pompon-like and composed of numerous homogenous nanocones which were radiated from one center. The length and diameter of nanocones were gradually decreased with the increase of doping amount, indicating the morphology of the samples could be well controlled by varying the Zn²⁺ concentration. Additionally, the feasible growth process of obtained samples was discussed on the basis of the habits of nucleation and crystal growth. The photocatalytic performances of Zn-doped SnO₂ hierarchical structures were systematically investigated in the degradation of methylene blue (MB), methyl orange (MO), rhodamine B (RhB) and Congo red (CR). Compared with pure SnO₂, the 4.0?wt% Zn-doped SnO₂ hierarchical structure presented superior photocatalytic ability, which could be mainly attributed to both present oxygen vacancies and doped Zn²⁺ centers. At last, the possible photocatalytic mechanism was studied by means of the active species trapping experiments as well as the calculated energy band structures.     

Development of niobium doped tin oxide nanostructure via hydrothermal route for photocatalytic degradation of methylene blue and antimicrobial study

In this work, we discuss the effect of niobium (Nb) doping concentrations of 2% and 4% on the physicochemical characteristics and photocatalytic properties of tin dioxide nanostructure, which were successfully developed by a basic hydrothermal route. Nb-doped SnO₂ were characterized with regards to their optical, structural and photocatalytic features. X-ray diffraction (XRD) analyses display that both pristine and doped tin dioxide had a fine crystalline structure having tetragonal structure. Scanning electron microscopy (SEM) analysis shows that materials exhibited the irregular shaped nanoparticles morphology. Optical absorption analysis using UV–visible spectroscopy revealed a redshift in the bandgap energy for Nb³⁺ doped SnO₂ nanoparticles. Methylene blue aqueous (MB) dye was degraded by 93.78% in 120 min when exposed to 4% Nb doped SnO₂ NPs under visible light. The 4% Nb doped SnO₂ shows elevated photocatalytic activity owing to their greater surface area containing greater active zones responsible for adsorption of larger dye species and good structural stability. Similarly, the 4% Nb doped SnO₂ photocatalysts maintained their excellent stability and photodegradation efficiency over 89% even after being subjected to 5th cycles. The scavenger analysis demonstrates that the superoxide (O₂) radical, a major active substance, performed a crucial role in the mineralization of the aqueous MB dye. The 4% Nb doped SnO₂ also shows remarkable antimicrobial activity. Our finding suggests that doping strategy considered as efficient method that can help to increase the photocatalytic and antimicrobial activity.     

Preparation and characterization of heteroepitaxial Zn2SnO4 single crystalline films prepared on MgO (100) substrates

Zinc stannate (Zn₂SnO₄) films were deposited on MgO (100) substrates by pulsed laser deposition, and Zn₂SnO₄ monocrystalline films were obtained by postannealing process. The structures, surface morphologies, and optical properties of the Zn₂SnO₄ films annealed at different temperatures were investigated in detail. Crystal structure analyses showed that the film annealed at 800°C was single crystal Zn₂SnO₄ with an inverse-spinel structure. The heteroepitaxial mechanism was further clarified by a schematic diagram, and the epitaxial relationships between the film and substrate were Zn₂SnO₄ (400) || MgO (200) with Zn₂SnO₄ [001] || MgO [001]. The obtained Zn₂SnO₄ films exhibited excellent transparency. The optical band gap of the 800°C-annealed Zn₂SnO₄ film was about 3.97 eV. The extinction coefficients and refractive indexes of the Zn₂SnO₄ films annealed at different temperatures as a function of wavelength were analyzed in detail.     

Solvothermal synthesis of porous conjugated polymer with high surface area for efficient adsorption of organic and biomolecules

Aimed to prepare high efficient dye sorbent and control water pollution, herein we utilized solvothermal method to synthesize porous polyimide (PI) polymer with a large surface area using DMSO as solvent. Unlike the solid-state thermal polymerized PI with low surface area of 5 m²g^?1, this PI material prepared in DMSO solvent possessed a large surface area of 430 m²g^?1, which was beneficial for adsorption of organic dye in waste water, achieving a max MO adsorption of 200 mg g^?1 three times higher than that of multiwalled carbon nanotube. The adsorption kinetics of dye molecules on PI was investigated in detail and the R² value of 0.99071 for pseudo-second-order model confirms the adsorption was fitted best with Langmuir isotherm.     

Hydrogen Production from Aqueous Solutions of Glycerol on TiO<Subscript>2</Subscript>/Ru-MCM-41 Photocatalysts Using Solar Light

Ru-MCM-41 molecular sieves were prepared (Si/Ru atomic ratio?=?50 or 100) by a hydrothermal method and impregnated with TiO₂. The materials were characterized by XRD, N₂ physisorption, DRS, SEM and TEM. Their potential application to hydrogen production by photolysis of water using solar light was tested in a batch reactor using mixtures of water and glycerol (0–6.85 mol L^?1) at pH varying from 1 to 11. The photocatalytic efficiency under simultaneous UV (0.05 μW cm^?2) and visible light (90.07 W m^?2) irradiation was compared to the activity of TiO₂/MCM-41 (i.e., no Ru incorporated) and commercial Degussa TiO₂ P25. The most active material was 20%TiO₂/Ru-MCM-41(100) whose performance (220.6 µmol g_Ti ^?1 H₂) was approximately 47 times higher than TiO₂ P25. Characterization results showed the deposition of TiO₂ and revealed the formation of RuO₂ on the surface. Hydrogen generation was improved due to higher charge separation at the TiO₂/RuO₂ heterojunction and to the enhancement of visible light absorption caused by surface plasmon resonance (SPR). Hydrogen production increased with glycerol concentration, tending to stabilize around 40.3 µmol h^?1 g_Ti ^?1 above 4 mol L^?1 of glycerol. Hydrogen generation reached its maximum at extreme values of pH (1 and 11).     

Activated carbon from cherry stones by chemical activation: Influence of the impregnation method on porous structure

Cherry stones are utilized as a precursor for the preparation of activated carbons by chemical activation with phosphoric acid (H₃PO₄). The activation process typically consists of successive impregnation, carbonization, and washing stages. Here, several impregnation variables are comprehensively studied, including H₃PO₄ concentration, number of soaking steps, H₃PO₄ recycling, washing of the impregnated material, and previous semi-carbonization. The choice of a suitable impregnation methodology opens up additional possibilities for the preparation of a wide variety of activated carbons with high yields and tailored porous structures. Microporous activated carbons with specific surface areas of ～800 m² g^?1 are produced, in which > 60% of the total pore volume is due to micropores. High surface areas of ～1500 m² g^?1 can be also developed, with micropore volumes being a 26% of the total pore volume. Interestingly, using the same amount of H₃PO₄, either carbons with surface areas of 791 and 337 m² g^?1 or only one carbon with a surface area of 640 m² g^?1 can be prepared. The pore volumes range very widely between 0.07–0.55, 0.01–0.90, and 0.09–0.79 cm³ g^?1 for micropores, mesopores, and macropores, respectively.