S.M. Lee

Photocatalytic reduction of Cr(VI) and Ni(II) in aqueous solution by synthesized nanoparticle ZnO under ultraviolet light irradiation: a kinetic study

Photocatalytic removal of Cr(VI) and Ni(II) from aqueous solution using synthesized nanoparticle ZnO under ultraviolet (UV) light irradiation was studied in this work. Firstly, nanoparticle ZnO was prepared by the chemical method with an organic chemical inhibitor. Then removal efficiency of Cr(VI) and Ni(II) by nanoparticle ZnO was investigated with variation of the solution pH, ZnO dosage, contact time and initial Cr(VI) and Ni(II) concentration. Maximum removal of Cr(VI) and Ni(II) was observed at near‐neutral pH because the reduced photocatalytic activity of ZnO at exceedingly low and high pH values originates from either acidic/photochemical corrosion of the catalyst and/or surface passivation with Zn(OH)2. As the ZnO dosage increased, the removal efficiency of Cr(VI) and Ni(II) was continuously enhanced, but was gradually decreased above 1.25 g/l due to the increased blockage of the incident UV light used for the photocatalytic reaction. The optimum ZnO dosage was determined as 1 g/l. Removal efficiencies of Cr(VI) and Ni(II) decreased as initial Cr(VI) and Ni(II) concentration increased, due to an increased inhibition effect on the surface of ZnO resulting from the decreased reaction sites on the surface of ZnO required for the further photocatalytic reaction.

Photocatalytic removal of Cr(VI) with illuminated TiO2

Abstract The effect of dissolved oxygen on the photocatalytic reduction of Cr(VI) with illuminated TiO2 was studied in this work with variation of the solution pH, contact time, and initial Cr(VI) concentration. Oxygen or nitrogen gas was used as a purging gas. Overall, the removal efficiency of Cr(VI) decreased as the solution pH increased. The removal of Cr(VI) by UV/TiO2 increased by decreasing the solution pH because of the increased potential difference between the conduction band of TiO2 and Cr(VI)/Cr(III) as well as the anionic-type adsorption of Cr(VI) onto the TiO2 surface. The removal efficiency of Cr(VI) increased in purging of nitrogen gas compared to that of oxygen gas because of less competition between dissolved oxygen and Cr(VI) in the reaction with the electron in the conduction band of TiO2. The reduction pattern was better described by the first-order kinetic model.

Effect of different types of organic compounds on the photocatalytic reduction of Cr(VI).

The effect of different types of organic compounds (humic acid, oxalate, ethylenediaminetetraacetic acid, nitrilotriacetic acid, phenol) on the photocatalytic reduction of Cr(VI) with illuminated TiO2 was studied in this work with variation of the solution pH, contact time, initial Cr(VI) concentration and type of organic compounds. As the pH increased, the removal efficiency for Cr(VI) decreased. The increase in Cr(VI) removal by UV/TiO2 with decreasing solution pH was due to the increased potential difference between the conduction band of TiO2 and Cr(VI)/Cr(III) as well as the anionic-type adsorption of Cr(VI) on to the TiO2 surface. Removal efficiency for Cr(VI) increased in the presence of organic compound compared with that without organic compound because positive holes in the TiO2 were scavenged by organic additives. The reduction pattern of Cr(VI) was better described by the first-order kinetic model. Finally photocatalytic reaction with illuminated TiO2 can be effectively applied to treat wastewater contaminated with Cr(VI).

Photocatalytic removal of cyanide with illuminated TiO2

Effects of TiO(2) dosage, pH and initial cyanide concentration on the removal efficiency of cyanide from aqueous solutions with illuminated TiO(2) have been investigated. Adsorption and oxidation were recognized as significant processes for the elimination of cyanide. From the Langmuir isotherm, the maximum adsorption capacity was determined as 17.24 mg/g at pH 7. Adsorbed amount of cyanide slightly increased as the TiO(2) dosage increased. However, as no significant increase was observed above 1 g/L TiO(2), an optimum TiO(2) dosage was determined as 1 g/L. Photocatalytic oxidation efficiency of cyanide was greatly affected by the solution pH. It increased as the solution pH decreased. The photocatalytic oxidation efficiency after 120 min was 80.4% at pH 3 while it was only 20.4% at pH 11. Photocatalytic oxidation of cyanide was well described by the second-order kinetics. Photocatalytic reaction with illuminated TiO(2) can be effectively applied to treat industrial wastewater contaminated with cyanide.

Effect of different type of organic compounds on the photocatalytic reduction of Cr(VI) in presence of ZnO nanoparticles

ABSTRACTEffect of different type of organic compounds (humic acid, oxalate, ethylenediaminetetraacetic acid, nitrilotriacetic acid, phenol) on the photocatalytic reduction of Cr(VI) with illuminated ZnO was studied in this work with variation of solution pH, contact time, initial Cr(VI) concentration, and type of organic compounds. Maximum removal of Cr(VI) was observed at near neutral pH because of the reduced photocatalytic activity of ZnO at exceedingly low and high pH values originated from either acidic/photochemical corrosion of the catalyst and/or surface passivation with Zn(OH)2. Removal efficiency of Cr(VI) increased in the presence of oxalate compared to that without presence of organic compound because of positive holes in the valence band of ZnO were scavenged by oxalate. However, it was decreased in the presence of the other organic compounds due to the blocking effects of electron transfer between ZnO surface and Cr(VI). The reduction pattern of Cr(VI) was better described by first-order kin...

Application of Fe(VI) in the treatment of Zn(II)‐NTA complexes in aqueous solutions

The higher oxidation state of iron, i.e. Fe(VI), was exploited to treat the synthetic wastewater containing Zn(II)‐NTA. The decomposition of Zn(II)‐NTA by Fe(VI) was investigated with the help of analytical data obtained for the change in Fe(VI) concentration, dissolved organic carbon (DOC) and total soluble Zn(II) concentration as a function of time at various concentrations of Zn(II)‐NTA and at constant Fe(VI) concentration. The UV‐Visible data was used to explain the reaction kinetics for redox reactions between Fe(VI) and Zn(II)‐NTA. The pseudo‐first‐order rate constant was calculated keeping the Zn(II)‐NTA concentration in excess and hence the overall second‐order‐rate constant was obtained. Fe(VI) reduction was almost unaffected with the 1000 times increase in ionic strength (NaNO3), as well as in the presence of completely oxidized background electrolytes. However, Fe(VI) reduction was greatly affected in the presence of both SO3 2− and NO2 − especially at higher concentrations, indicating a competitive reduction took place between Zn(II)‐NTA and Na2SO3 or NaNO2 in the Fe(VI) treatment. These results were again supported by the dissolved organic carbon observations since relatively very low removal of the dissolved organic carbon occurred in the presence of Na2SO3 and NaNO2.

Comparison between a moving bed bioreactor and a fixed bed bioreactor for biological phosphate removal and denitrification.

Moving bed bioreactors (MBBR) and fixed bed bioreactors (FBBR) were compared for biological phosphorus removal and denitrification. The sorption denitrification P-elimination (S-DN-P) process was selected for this study. Results indicated that all nutrients were removed by the FBBR process compared with the MBBR process: 19.8% (total COD), 35.5% (filtered COD), 27.6% (BOD(5)), 62.2% (acetate), 78.5% (PO(4)-P), and 54.2% (NO(3)-N) in MBBR; 49.7% (total COD), 54.0% (filtered COD), 63.2% (BOD(5)), 99.6% (acetate), 98.6% (PO(4)-P), and 75.9% (NO(3)-N) in FBBR. The phosphate uptake and NO(3)-N decomposition in the FBBR process during the denitrification phase were much higher than for the MBBR process despite being of shorter duration. Results obtained from this study are helpful in elucidating the practical implications of using MBBR and FBBR for the removal of bio-P and denitrification from wastewater.

Treatment of wastewater contaminated with Cd(II)–NTA using Fe(VI)

Abstract The aim of the present investigation is to assess the applicability of Fe(VI) in the treatment of simulated wastewater contaminated with Cd(II)–nitrilotriacetic acid (NTA) soluble species as a cleaner and greener treatment technology. Initially, the degradation of NTA was observed in a single system treatment reactor that applied varied doses of NTA. Results were correlated with the change in Fe(VI) concentration measured by UV–visible spectrophotometer. As a next step, the Fe(VI) was introduced in the reaction reactor containing Cd(II)–NTA species as to investigate the degradation of NTA measured with the help of change in total organic carbon (TOC). The NTA degradation was observed by using the TOC values obtained at different time intervals at pH 10.0. Moreover, the treated samples were subjected to the change in total cadmium concentration as to observe the simultaneous removal of cadmium from the aqueous solutions. The reactivity of the Fe(VI) was also assessed varying the pH from 8.0 to 12....

Rapid and efficient removal of boron from deep sea water using synthesized polymer resin

AbstractThe present investigation aims to remove boron from deep sea water using the n-methyl d-glucamine-modified polymeric resin as synthesized in the laboratory. The resins are characterized by IR analysis and the morphology is discussed with the help of scanning electron microscopic images. Further, the resin is distributed in three different bead sizes i.e. 0.25, 0.5 and 1.0 mm, and assessed their removal efficiency for the boron removal under batch and column operations. Batch data show that a very fast uptake of boron took place and within 20 min of contact, almost a complete removal of boron occurred. Further, the kinetics of boron uptake is performed using linear equations of pseudo-first-order and pseudo-second-order rate equations. The applicability of pseudo-second-order rate law inferred that the boron is sorbed onto the solid surface by strong chemical forces, forming an “inner sphere complexes”. The batch and column data obtained for the boron removal is then critically compared with the co...

Synthesis of TiO2 using sol-gel method and comparison of photocatalytic characteristics

Abstract The aim of the present communication is to compare the physical and chemical properties of TiO2 powder and TiO2 coated thin film particularly the photochemical degradation of pollutants. TiO2 Powder was synthesized by the sol–gel method and was annealed with the temperatures ranging from 300 to 1100°C. TiO2 coating, about 8 μm thin film, was successfully fabricated by the sol–gel dip process on borosilicate glass used as a substrate having a surface area of 100 mm2 and was further annealed at the same temperatures 300–1100°C. TiO2 films and powder which were annealed at 300°C for 2 h have the structure of anatase and the particle phase composition was mainly dependent to the annealing temperature which was found to be changed from amorphous to crystalline anatase and rutile by increasing the temperature. These results were demonstrated based on the X-ray diffraction, SEM and UV–visible spectroscopic data. Further, the photocatalytic characteristics of the synthesized powder and film showed that t...