Several zirconium-based metal-organic frameworks (Zr-MOFs) have been synthesized using ammonium hydroxide as an additive in the synthesis process. Their physicochemical properties have been ...characterized by N(2) adsorption/desorption, XRD, SEM, FTIR, and TGA, and their application in CO(2) adsorption was evaluated. It was found that addition of ammonium hydroxide produced some effects on the structure and adsorption behavior of Zr-MOFs. The pore size and pore volume of Zr-MOFs were enhanced with the additive, however, specific surface area of Zr-MOFs was reduced. Using an ammonium hydroxide additive, the crystal size of Zr-MOF was reduced with increasing amount of the additive. All the samples presented strong thermal stability. Adsorption tests showed that capacity of CO(2) adsorption on the Zr-MOFs under standard conditions was reduced due to decreased micropore fractions. However, modified Zr-MOFs had significantly lower adsorption heat. The adsorption capacity of carbon dioxide was increased at high pressure, reaching 8.63 mmol g(-1) at 987 kPa for Zr-MOF-NH(4)-2.
•Raw and chemically treated Eucalyptus sheathiana bark were used in Zn2+ removal.•The factors that affect the adsorption process were investigated in detail.•Both Freundlich and Langmuir isotherm ...models are applicable.•The eucalyptus bark show great potential to treat metal ion bearing wastewaters.
In this study, potential application of abundantly available agricultural by-product Eucalyptus sheathiana bark in its raw and sodium hydroxide (NaOH) modified form to remove Zn2+ from its aqueous solutions was investigated by considering parameter identification and optimization, reusability, equilibrium, kinetic and thermodynamic studies. The adsorbent was characterized by SEM-EDX, FTIR, XRD, BET surface area and bulk density and point of zero charge were also determined. The process was strongly pH dependent and the adsorption percentage of Zn2+ was increased with an increase in solution pH from 2.5 to 5.1. Conversely, the adsorption percentage of Zn2+ decreased with the increase in adsorbent dosage, initial metal concentration, temperature and ionic strength. Kinetic measurements showed that the process was multistep, rapid and diffusion controlled. It was found to follow the pseudo-second-order rate equation. Equilibrium adsorption studies showed that both Freundlich and Langmuir models are applicable for both raw and base modified eucalyptus bark. MPSD error function was used to treat the equilibrium data using non-linear optimization technique for evaluating the fit of the isotherm equations. The maximum sorption capacity of modified eucalyptus bark was 250.00mg/g at 30°C which was comparative to other adsorbents. Various thermodynamic parameters indicate that the process was spontaneous and physical in nature. Desorption studies were also performed to determine possible recovery potential of Zn2+ and the re-usability of the biomass and to identify the mechanism of adsorption.
In heterogeneous catalysis for water treatment, feasible recovery of nanocatalysts is crucial to make the process cost-effective and environmentally benign. In this study, we applied two strategies, ...for example, magnetic separation and hierarchical structure of solid catalysts, to ensure manganese catalysts are readily separable, meanwhile their catalytic performance was retained by the nanosized structure of MnO2 nanosheets or nanorods. ZnFe2O4 was used as the magnetic core and MnO2 corolla-like sphere consisting of nanosheets, and sea-urchin shaped structure made of nanorods, were fabricated by a hydrothermal method at 100 and 140 °C, respectively. Crystalline structure, morphology and textural property of the materials were investigated. The prepared catalysts were able to effectively activate peroxymonosulfate (PMS) to generate sulfate radicals for catalytic oxidation of a typical organic pollutant of phenol. After the heterogeneous catalysis, the catalysts were easily recovered by applying an external magnetic field. The effects of temperature and repeated use on the degradation efficiencies were evaluated. The generation and evolution of sulfate radicals and phenol oxidation were studied using both competitive radical tests and electron paramagnetic resonance (EPR).
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► A solution method was employed to prepare metal ion doped BiTaO4 photocatalysts. ► BiTaO4 doped with La, Ga and Nd catalysts showed better and stable activity than TiO2 under both ...UV and visible light. ► Metal ion doped BiTaO4 catalysts showed good performance in methylene blue degradation.
Various metal ions (Al, Nd, La, Ga, Ba, Sn, W, Fe, Co, Cr, Ce, Cu, Sb, Pb, Ni, Ag) doped and undoped triclinic BiTaO4 photocatalysts were synthesized using a solution method. The prepared materials were characterized with high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and UV–vis diffuse reflectance spectroscopy. BiTaO4 doped with various metal ions were tested for photocatalytic oxidation of water and air contaminants with both UV and visible light irradiation. Metal ion doping changed the photophysical properties, but did not alter the crystalline structure of BiTaO4. Enhanced photocatalytic oxidation of toluene in air was observed for dopants such as Al, Nd, La, Ga, Ba, Sn, W, Fe, Sb, Ag, while other metal ions like Cu, Ce, Co, Pb, and Ni induced a detrimental effect on the photocatalytic performance. BiTaO4 doped with La, Ga and Nd catalysts showed much better and stable performance than TiO2 in gaseous toluene oxidation with both UV and visible light. Some metal ion doped BiTaO4 catalysts also have shown good performance in methylene blue degradation in water.
•Metal (Fe, Ni, Ag, or Pt) and N codoped TiO2 photocatalysts were successfully synthesized.•The visible light absorbance of TiO2 was significantly improved by co-doping.•N–Pt–TiO2 showed the highest ...phenol degradation under visible lights at λ>490nm.•A synergetic effect of Pt and N makes the enhanced photocatalytic activity.
Various cation and nitrogen doped and codoped TiO2 photocatalysts, such as N–TiO2, Pt–TiO2, N–Fe–TiO2, N–Ni–TiO2, N–Ag–TiO2 and N–Pt–TiO2, were prepared by an acid-catalysed sol–gel process. The photocatalysts were characterised by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, UV–visible diffuse reflectance absorption spectroscopy (UV–vis DRS), and X-ray photoelectron spectroscopy (XPS). The activities of the photocatalysts were evaluated in photodegradation of phenol solutions under simulated sunlight irradiations. A negative effect of some transition metals (iron and nickel) on photocatalysis was observed on N-metal codoped TiO2, while enhancements in photocatalysis from noble metals (silver and platinum) were obtained. N–Pt codoped TiO2 showed a higher activity under UV–vis irradiations than Degussa P25, with an enhancement of 5.9times higher. The synergistic effect of N–Pt-codoping was ascribed to the multivalent states of platinum. In addition, photocatalytic activity of N-, Pt-doped and N–Pt-codoped materials were further investigated under visible light irradiations with λ>430nm and λ>490nm. This study therefore demonstrated a promising strategy for design of highly efficient photocatalysts for remediation of aqueous pollutants.
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•Magnetic Fe/C core/shell supported Mn catalysts were synthesized by redox reaction.•The supported Mn catalysts showed a higher phenol oxidation than commercial MnO2.•Magnetic Mn ...catalysts are promising in water treatment and separation.
Magnetic separation is more cost-effective than conventional separation processes in heterogeneous catalysis, especially for ultrafine nanoparticles. Magnetic core/shell nanospheres (MCS, Fe3O4/carbon) were synthesized by a hydrothermal method and their supported manganese oxide nanoparticles (Mn/MCS) were obtained by redox reactions between MCS and potassium permanganate at a low temperature. The materials were analyzed by a variety of characterization techniques such as powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N2 adsorption/desorption. The Mn/MCS catalysts were able to effectively activate Oxone® for phenol degradation in aqueous solutions. Nitrogen treated MCS supported Mn achieved 100% conversion within 120min. Kinetic studies showed that phenol degradation over supported Mn catalysts follows the first order kinetics. It was also found that the catalysts can be easily separated from the aqueous solutions by an external magnetic field. The Oxone® activation mechanism by Mn/MCS catalysts was discussed and sulfate radicals were suggested to be the primary reactive species generated from peroxymonosulfate (PMS) for phenol catalytic oxidation.
Scanning electron microscopy of struvite; (a) seed crystals; (b) product crystal at pH 9, 25°C and 120rpm. Display omitted
•Struvite crystal growth depends on various physico-chemical process ...parameters.•Struvite crystal formation followed a diffusion–reaction mass transfer mechanism.•Mass transfer coefficients of struvite crystallisation has been determined.•Various growth kinetics parameters have been determined.
In response to struvite formation problems in wastewater treatment plants (WWTP), this mechanistic growth kinetic study of struvite crystal (MgNH4PO4·6H2O) was undertaken to determine the cause of preferential accumulation and to provide the remediation information to the designer of WWTP. Struvite is the mineral phase of one of the urinary tract stones of human and animals also. Here the authors presented the struvite crystal growth formation kinetics mechanism under different physico-chemical process parameters such as supersaturation (Mg2+,NH4+,PO43-), solution pH, stirrer speed, temperature, impurities and seeding conductions. To measure the growth rate of struvite crystals and to identify its various dependence system parameters, laboratory measurements were conducted in an isothermal batch 1l stirred seeded crystalliser. Supersaturation and pH have been found to be the most influential parameters for struvite crystallisation. It was found that growth rate increased with an increase in solution pH in the pH range of 8–9. The rate of change of ortho-phosphate concentration in the bulk solution increases with increasing supersaturation ratio. The growth rate increased with increase in temperature. Higher NaCl salt concentration and higher speed also produced higher struvite growth kinetics. Fundamentally struvite crystal formation followed a classical diffusion–reaction mass transfer mechanism and overall mass transfer coefficients (KL) under various physico-chemical process parameters have been determined. The kinetic rate constants were also calculated by fitting a first-order kinetic model and power law model to the experimental data obtained. It was also found that there was increase in product crystal size with increase in solution pH, stirrer speed and amount of salts due to slow nucleation followed by fast growth process. Struvite crystallisation may also have implication in an alternative sustainable and economical recovery of phosphorous from concentrated waste water stream.
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► Red mud (RM) and fly ash (FA) were used for synthesis of supported Co catalysts. ► Co/RM presented higher activity than Co/FA in oxidation of phenol. ► Phenol degradation on Co/RM ...and Co/FA followed first order kinetics.
Industrial wastes, red mud (RM) and fly ash (FA), were employed as supports for synthesis of Co-oxide based catalysts. Co/RM and Co/FA were characterised by X-ray diffraction (XRD), scanning electron microscopy coupling with energy dispersive spectroscopy (SEM-EDS), elemental mapping, and UV–vis diffuse reflectance spectroscopy. Their catalytic activity in oxone activation for phenol degradation for wastewater treatment was tested. It was found that Co oxide on the catalysts was present in the Co3O4 phase and the oxide showed better dispersion on RM. Co/FA and Co/RM could degrade phenol with the presence of oxone and Co/RM exhibited much higher activity than Co/FA, due to high dispersion of Co oxide and surface basicity of RM. Higher oxone concentration in solution enhanced phenol degradation efficiency and reaction temperature also promoted phenol degradation. Kinetic studies showed that phenol degradation followed first order kinetics and the activation energies on Co/RM and Co/FA were found to be 66.3 and 47.0kJ/mol, respectively.
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