Solar photocatalytic degradation of 4-chlorophenol: Mechanism and kinetic modelling

The present study reports a mechanism and kinetic model of solar photocatalytic degradation of 4-chlorophenol (4-CP) and its intermediates based on the experimental results. Three intermediate compounds hydroquinone (HQ), 4-chlorocatechol (4cCat) and phenol were found during the solar degradation of different 4-CP concentrations using 0.5 g/L TiO2 as a photocatalyst. In order to obtain more details about the photocatalytic reaction pathway and the kinetic model, set of experiments were carried out using the major intermediates (HQ and 4cCat) as model reactants. To minimise the number of variables and give more accuracy to the kinetic model, the adsorption constants of 4-CPand its intermediates were obtained experimentally. The reaction mechanism for the photocatalytic degradation of 4-CP is proposed. The proposed model predicts well the concentrations of 4-CP and its by-products during the solar photocatalytic degradation at different initial concentrations. The model provides a very good fit of the experimental data and works for a wide range of 4-CP initial concentrations (25–100 mg/L)

Co3O4 nanocrystals with predominantly exposed facets: Synthesis, environmental and energy applications

Facet-dependent properties of novel metal or metal-oxide nanocrystals were discovered recently, and are attracting intensive interest owing to their great potential for various practical applications. Co3O4 as an important transition metal oxide shows electronic, magnetic, and redox properties which have found many applications in energy conversion and storage, magnetic separation, sensor devices and catalysis. This review summarizes the most recent research advances in synthesis and applications of nanosized Co3O4 with predominantly exposed facets, with emphasis on the enhanced performances in catalysis and electrochemical properties. The mechanism for improved selectivity and activity was discussed, and a panorama of the correlations between particle shape, crystal plane, surface atom arrangement, and active sites has been drawn. Insightful findings in this scope may be achieved by forthcoming research in theoretical calculations, rational synthesis, and emerging applications. Thus, researchers can manipulate the synthesis at the atomic level resulting in novel applications of the materials in a wide variety of areas

Amino-functionalized Zr-MOF nanoparticles for adsorption of CO2 and CH4

Amino-functionalized Zr-MOF (amino-Zr-MOF) was synthesized using 2-aminoterephthalic acid as an organic linker. The physicochemical properties of the material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption to understand its crystalline structure, morphology, thermal stability, and porous structure. CO2 adsorption isotherms on amino-Zr-MOF were obtained at 1 atm and at different temperatures. In addition, CO2 and CH4 adsorption at high pressure (up to 10 atm) was also measured. CO2 adsorption capacity on amino-Zr-MOF was 9 mmol/g at 988 kPa, 0°C, while CH4 adsorption capacity was 3.7 mmol/g at 900 kPa, 0°C. The heat of CO2 adsorption on amino-Zr-MOF was estimated to be 29.4 kJ/mol. Continuous column tests of CO2 adsorption were performed at different concentrations of CO2 in nitrogen at 20 mL/min and 0.7 g adsorbent and total adsorbed amounts of CO2 within the column during the breakthrough time were calculated to be 4.55, 5.26 and 4.37 mmol/g at 10%, 15% and 20%CO2, respectively

Effect of combined microwave-ultrasonic pretreatment on anaerobic biodegradability of primary, excess activated and mixed sludge

This work deals with the effect of combined microwave-ultrasonic pretreatment on the anaerobic biodegradability of primary, excess activated and mixed sludge. The characteristics, biodegradability and anaerobic digester performance for untreated primary, excess activated and mixed sludge were compared to combined microwave-ultrasonic pretreated primary, excess activated and mixed sludge. All sludge samples were subjected to Microwave treatment at 2450 MHz, 800 W and 3 min followed by ultrasonic treatment at a density of 0.4 W/mL, amplitude of 90%, Intensity of 150 W, pulse of 55/5 for 6min. Methane production in pretreated primary sludge was significantly greater (11.9 ml/g TCOD) than the methane yield of the untreated primary sludge (7.9 ml/g TCOD). Cumulative methane production of pretreated Excess Activated Sludge (EAS) was higher (66.5 ml/g TCOD) than the methane yield from pretreated mixed sludge (44.1 ml/g TCOD). Furthermore, digested EAS showed significantly higher dewaterability (201 s) than digested primary sludge (305 s) or mixed sludge (522 s). The average Methane: Carbondioxide ratio from EAS (1.85) was higher than that for mixed untreated sludge (1.24). VS reduction was also higher for EAS than the other two sludge types. However, pretreatment of EAS resulted in significant reduction in dewaterability due to higher percentage of fine floc particles in the pretreated EAS

Manganese oxides at different oxidation states for heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions

A series of manganese oxides (MnO, MnO2, Mn2O3 and Mn3O4) were synthesized and tested in heterogeneous activation of peroxymonosulfate (PMS) for phenol degradation in aqueous solutions. Their properties were characterized by several techniques such as X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and N2 adsorption/desorption isotherms. Catalytic activities of Mn oxides were found to be closely related to the chemical states of Mn. Mn2O3 is highly effective in heterogeneous activation of PMS to produce sulfate radicals for phenol degradation compared with other catalysts (MnO, MnO2, and Mn3O4). The activity shows an order of Mn2O3> MnO > Mn3O4> MnO2. Mn2O3 could completely remove phenol in 60 min at the conditions of 25 mg/L phenol, 0.4 g/L catalyst, 2 g/L PMS, and 25?C. After heat regeneration, the activity could be fully recovered. A pseudo first order model would fit to phenol degradation kinetics and activation energy was obtained as 11.4 kJ/mol

Visible light responsive titania photocatalysts codoped by nitrogen and metal (Fe, Ni, Ag, or Pt) for remediation of aqueous pollutants

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) onphotocatalysis 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 5.9 times 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 lambda > 430 nm and lambda > 490 nm. This study therefore demonstrated a promising strategy for design of highly efficient photocatalysts for remediation of aqueous pollutants

A comparative study of spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles in catalytic oxidation of phenolic contaminants in aqueous solutions

Spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles were prepared, characterized, and tested in degradation of aqueous phenol in the presence of peroxymonosulfate. It was found that Mn3O4 and Co3O4 nanoparticles are highly effective in heterogeneous activation of peroxymonosulfate to produce sulfate radicals for phenol degradation. The activity shows an order of Mn3O4 > Co3O4 > Fe3O4. Mn3O4 could fast and completely remove phenol in about 20 min, at the conditions of 25 ppm phenol, 0.4 g/L catalyst, 2 g/L oxone®, and 25 °C. A pseudo first order model would fit to phenol degradation kinetics and activation energies on Mn3O4 and Co3O4 were obtained as 38.5 and 66.2 kJ/mol, respectively. In addition, Mn3O4 exhibited excellent catalytic stability in several runs, demonstrating that Mn3O4 is a promising catalyst alternative to toxic Co3O4 for water treatment

β-MnO2 ACTIVATION OF PEROXYMONOSULFATE FOR CATALYTIC PHENOL DEGRADATION IN AQUEOUS SOLUTIONS

β-MnO2 was prepared and used to activate peroxymonosulphate for degradation of aqueous phenol. The sample was characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM). The catalyst is highly effective in heterogeneous activation of PMS to produce sulfate radicals for phenol degradation compared with homogeneous oxidatiom. β-MnO2 could completely remove phenol in 30 min at the conditions of 25 ppm phenol, 0.4 g/L catalyst, 2 g/L PMS, and 25 oC. A pseudo first order model would fit to phenol degradation kinetics and activation energy was obtained as 38.2 kJ/mol

Rheological Characteristics of Municipal Thickened Excess Activated Sludge (TEAS): Impacts of pH, Temperature, Solid Concentration and Polymer Dose

Rheological characterization of sludge is known to be an essential tool to optimize flow, mixing and other process parameters in wastewater treatment plants. This study deals with the characterization of thickened excess activated sludge in comparison to raw primary sludge and excess activated sludge. The effects of key parameters (total solid concentration, temperature, and pH) on the rheology and flow behavior of thickened excess activated sludge were studied. The rheological investigations were carried out for total solid concentration range of 0.9–3.7 %w/w, temperature range of 23–55 °C, and pH range of 3.6–10.0. Different rheological model equations were fitted to the experimental data. The model equations with better fitting were used to calculate the yield stress, apparent, zero-rate, infinite-rate viscosities, flow consistency index, and flow index. The decrease in concentration from 3.7 to 3.1 %w/w resulted in a drastic reduction of yield stress from 27.6 to 11.0 Pa, while a further reduction of yield stress to 1.3 Pa was observed as solid concentration was reduced to 1.3 %w/w. The viscosity at higher shear rate (>600 s−1) decreased from 0.05 Pa·s down to 0.008 Pa·s when the total solid concentration was reduced from 3.7 to 0.9 %. Yield stress decreased from 20.1 Pa down to 8.3 Pa for the Bingham plastic model when the temperature was raised from 25 to 55 °C. Activation energy and viscosity also showed decreasing trends with increasing temperature. Yield stress of thickened excess activated sludge increased from a value of 6.0 Pa to 8.3 Pa when the pH was increased from 3.6 to 10.0. The effect of polymer dose on the rheological behavior of the thickening of excess activated sludge was also investigated, and the optimum polymer dosage for enhanced thickener performance was determined to be 1.3 kg/ton DS

Biophysics of Malarial Parasite Exit from Infected Erythrocytes

Upon infection and development within human erythrocytes, P. falciparum induces alterations to the infected RBC morphology and bio-mechanical properties to eventually rupture the host cells through parasitic and host derived proteases of cysteine and serine families. We used previously reported broad-spectrum inhibitors (E64d, EGTA-AM and chymostatin) to inhibit these proteases and impede rupture to analyze mechanical signatures associated with parasite escape. Treatment of late-stage iRBCs with E64d and EGTA-AM prevented rupture, resulted in no major RBC cytoskeletal reconfiguration but altered schizont morphology followed by dramatic re-distribution of three-dimensional refractive index (3D-RI) within the iRBC. These phenotypes demonstrated several-fold increased iRBC membrane flickering. In contrast, chymostatin treatment showed no 3D-RI changes and caused elevated fluctuations solely within the parasitophorous vacuole. We show that E64d and EGTA-AM supported PV breakdown and the resulting elevated fluctuations followed non-Gaussian pattern that resulted from direct merozoite impingement against the iRBC membrane. Optical trapping experiments highlighted reduced deformability of the iRBC membranes upon rupture-arrest, more specifically in the treatments that facilitated PV breakdown. Taken together, our experiments provide novel mechanistic interpretations on the role of parasitophorous vacuole in maintaining the spherical schizont morphology, the impact of PV breakdown on iRBC membrane fluctuations leading to eventual parasite escape and the evolution of membrane stiffness properties of host cells in which merozoites were irreversibly trapped, recourse to protease inhibitors. These findings provide a comprehensive, previously unavailable, body of information on the combined effects of biochemical and biophysical factors on parasite egress from iRBCs.Singapore. Agency for Science, Technology and ResearchSingapore-MIT AllianceGlobal Enterprise for Micro-Mechanics and Molecular MedicineNational University of SingaporeNational Institutes of Health (U.S.) (Grant R01 HL094270-01A1)National Institutes of Health (U.S.) (Grant 1-R01-GM076689-01)National Institutes of Health (U.S.) (P41-RR02594-18-24