Photocatalytic decolorization of auramine and its kinetics study in the presence of two different sizes titanium dioxide nanoparticles at various buffer and non-buffer media

doi:10.1016/j.jiec.2014.05.014

Journal of Industrial and Engineering Chemistry

Volume 21, 25 January 2015, Pages 1044-1050

https://doi.org/10.1016/j.jiec.2014.05.014 Get rights and content

Abstract

In this research, photocatalytic decolorization and its kinetics study of auramine dye at various aqueous buffer and non-buffer media using nano-titanium dioxide in two different sizes of 15 and 70 nm in a photocatalyic reactor under 400 W high pressure mercury lamp irradiation under aerobic condition is described. The effects of some physico-chemical parameters such as photocatalyst dosage, medium pH and irradiation time were investigated in the presence of two different nano-photocatalysts and then the results were compared with each other. Kinetics study of photocatalytic treatment of auramine dye resulted that the dye decolorization approximately follows a pseudo-first order kinetic behavior according to the Langmuir–Hinshelwood model. Ultimately, the observed rate constants, experimental half-times, adsorption constants and decolorization rate constants at surface at buffer and non-buffer media under aerobic conditions were evaluated.

Introduction

Undoubtedly, today the environmental pollutants are as important problems in the human society. Massive amounts of untreated organic pollutants from different industrial companies (especially industrial dyes) represent an increasing environmental danger due to toxicity and carcinogenic properties [1], [2], [3]. All attempts for removal of the chemical pollutants are considered as current active fields in green chemistry point of view. There are many ways for pollutants elimination such as adsorption on activated carbon, ultrafiltration, reverse osmosis, coagulation by chemical agents, ion exchange on synthetic adsorbent resins and etc. [4], [5]. These methods generally cause transferring the organic pollutants from water to other media that naturally produce a new pollution. Therefore further treatment of the used adsorbent is required to regenerate it which will induce more cost to the removal processes. One of the effective low cost ways is photocatalytic degradation [6], [7], [8], [9], [10], [11], [12] that applies irradiation and semi-conductor oxides to eliminate the pollutant materials. The aim of photocatalysis process is effectively eliminating of the toxic materials from wastewaters under mild conditions [13]. Among many proposed semiconductors for photocatalytic treatment, titanium dioxide is a suitable photocatalyst because of its acceptable band gap energy, easily availability and low cast [14]. Such photocatalysts apply UV or visible light to generate electron–hole pairs at their conduction and valence bands [15]. Then the electrons in conduction band react with molecular oxygen in bulk solution to generate active oxidant species such as superoxide radical anions and hydrogen peroxide. On the other hand, the holes at valence band can oxidize surface hydroxyl groups to form OH radicals or even organic pollutant molecules. The mentioned oxidant species attack to the organic pollutant targets leading to eventually oxidation of them to CO₂, H₂O, and etc. Auramine as a diarylmethane dye is an industrial dye [16] that because of its stability in the nature is environmentally dangerous in human health point of view. The extra deaths from bladder cancer have been caused in people by use of this dye [17], [18], [19]. Therefore, degradation of this dye may be of interested for environmental researchers. The auramine dye is found in two chemical formula: not-salted(trade name: auramine O base) and mono-hydrochloride salt (trade name: auramine O). There are some reports on photocatalytic degradation of auramine hydrochloride [20], [21], [22], [23] under sunlight or low Pressure irradiation but to the best of our knowledge, there is no report on photocatalytic decolorization and its kinetics of not-salted auramine under high pressure mercury lamp at various buffer or non-buffer pHs using nano-titanium dioxide(anatase) under aerobic conditions. In continuation of our previous studies on dye removal [24], [25], [26], [27], [28], [29], in this work, we report photocatalytic decolorization and kinetic studies of auramine at various aqueous buffer and non-buffer solutions using nano-titanium dioxide in two different sizes of 15 and 70 nm in a photocatalyic reactor equipped with 400 W high pressure mercury lamp under aerobic condition. Furthermore the kinetics behavior of photocatalytic process was studied and then kinetics parameters were evaluated at all conditions.

Section snippets

Chemicals

Auramine (C₁₇H₂₁N₃, Yellow powder, C. I. 41000B), and other chemicals such as NaOH, HCl, KCl, K₂HPO₄, KH₂PO₄, Na₂B₄O₁₀.10 H₂O were purchased from Merck, Fluka and/or Aldrich. Two different sizes nano-Titanium dioxide (anatase) with average sizes of 15 and 70 nm (from Sigma-Aldrich) were used for all photocatalytic experiments. The SEM and TEM of these nanoparticles are illustrated at (Fig. 1).

Apparatus

SEM and TEM of titanium dioxide nano-particles were recorded on instruments of Hitachi Japan-S4160,

The effect of catalyst dosage

The a photocatalytic decolorization of auramine solution at each pH (pH_s of 5, 7 and 9) was performed both at buffer and non-buffer media with different dosages of nano-titanium dioxide for two different sizes (15 and 70 nm) at the same conditions under high pressure 400 W mercury lamp irradiation at room temperature. Fig. 2, Fig. 3 show the residual absorbance as a function of irradiation time in the presence of different dosages of photocatalysts at all above buffer and non-buffer pH_s. It was

Conclusion

In this research, photocatalytic decolorization of auramine dye was investigated in the presence of nano-titanium dioxide in two different sizes (15 and 70 nm). The effects of UV light (400 W high pressure Hg lamp), buffer and non-buffer pH_s, irradiation time and nano-titanium dioxide amount (in two different sizes) were examined. After appointment of suitable catalyst amount, photocatalytic decolorization of Auramin in water was performed under UV light irradiation. Based on the resultants data

Acknowledgments

Partial support of this work by Yasouj University is acknowledged.

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Photocatalytic decolorization of auramine and its kinetics study in the presence of two different sizes titanium dioxide nanoparticles at various buffer and non-buffer media

Abstract

Introduction

Section snippets

Chemicals

Apparatus

The effect of catalyst dosage

Conclusion

Acknowledgments

Appl. Catal., B: Environ.

Appl. Catal., B: Environ.

J. Hazard. Mater.

Appl. Catal., B: Environ.

J. Photochem. Photobiol., A: Chem.

Appl. Catal., B: Environ.

Catal. Today

J. Mol. Catal. A: Chem.

Appl. Catal., B: Environ.

J. Photochem. Photobiol., C: Photochem. Rev.

Desalination

Dyes Pigm.

J. Hazard. Mater.

Appl. Catal., B Environ.

Chemosphere

J. Hazard. Mater. B

Appl. Catal., B: Environ.

J. Catal.

Dyes Environmental Chemistry” in Kirk–Othmer Encyclopedia of Chemical Technology