Preparation and photocatalytic activity of nano-sized nickel molybdate (NiMoO4) doped bismuth titanate (Bi2Ti4O11) (NMBT) composite

https://doi.org/10.1016/j.jallcom.2007.09.015Get rights and content

Abstract

Various compositions of nano-sized (NiMoO4)x-doped Bi2Ti4O11 (x = 0.01, 0.05, 0.1) composites have been prepared by chemical solution decomposition (CSD) method using triethanolamine (TEA) as complexing agent. Ni(II) is one of reactive species on the catalyst surface and Mo(VI) ion helps to compensate the charge of the lattice. The photocatalysts based on the above compositions have been tested for photobleaching of methyl orange (MO) solution under Hg-lamp. The prepared nanopowders are characterized by XRD, EDAX, UV–vis spectra, specific surface area (BET), zeta potential, ESR and HRTEM analyses. The average particle size of nickel molybdate-doped bismuth titanate lies around 30 ± 2 nm measured from TEM. Result shows nickel molybdate-doped bismuth titanate (NiMoO4)x(Bi2Ti4O11)1−x (NMxBT1−x; x = 0.01) composite is found to be more photoactive compared all the compositions studied except degussa P25 titania.

Introduction

Recently, photocatalytic oxidation has been widely studied as a promising methodology for wastewater treatment or cleaning polluted air by using TiO2 powder [1]. TiO2 shows active photocatalyst for oxidation of organic compound in presence of air. Thus it can easily degrade different kinds of organic pollutants such as various dyes, pesticides, surfactants, and volatile organic compounds under UV-light irradiation [2], [3], [4], [5], [6], [7], [8]. Furthermore, such oxidation processes are activated at normal temperature and pressure. Suspended TiO2 particles have been largely used as efficient catalyst for the decomposition of organic contaminants present in water and aqueous wastes [9], [10]. However, the low efficiency for the utilization of visible light and the fast recombination between the photogenerated electrons and holes are often two major limiting factors which obstacle the improvement of photocatalytic activity of TiO2 [1]. It is therefore, of interest to develop a new photocatalysts with higher photocatalytic activity. In an earlier study, Yao et al. has found that Bi12TiO20 and perovskites Bi4Ti3O12 shows high-photocatalytic activity against methyl orange [11], [12]. It is demonstrated that the dopant ions or oxides can increase the quantum efficiency of the heterogeneous photocatalytic property by acting as an electron/hole traps or by altering the e/h+ pair recombination rate is an effective way to enhance the photocatalytic activity [13], [14], [15], [16], [17], [18], [19], [20].

In this present investigation, authors have studied the effect on the photocatalytic activity on methyl orange using Hg-vapor lamp and nickel molybdate (NiMoO4) incorporated Bi2Ti4O11 composites. These composite materials were prepared by chemical solution decomposition (CSD) method. NiMoO4 has been chosen because Ni2+ is good trap of photogenerated hole converting it to Ni3+, which is a good oxidant of organic molecule through formation of carbocataion. This study investigates detailed comparative photocatalytic properties of NiMoO4, Bi2Ti4O11, P25 titania and Bi2Ti4O11-doped with different amount of NiMoO4. The study shows that 1 mol% doping level has better photocatalytic properties in comparison to the other doping levels of NiMoO4 as well as the individual components. This study also includes the dependence of photocatalytic properties on pH and heat-treatment temperature of the doped materials along with the detailed characterization by XRD, EDAX study, HRTEM, zeta potential, ESR, UV–vis spectra and BET surface area.

Section snippets

Chemicals required

Titanium dioxide, Ni(NO3)2·6H2O, (NH4)2MoO4, Bi(NO3)3·5H2O, HNO3 (65%), NH4OH (25%), HF (40%), tartaric acid, triethanolamine (TEA), methyl orange (MO), were A.R. reagents from B.D.H. of India.

Preparation for nano-sized photocatalysts

For the synthesis of Bi2Ti4O11, Ni/Mo-doped Bi2Ti4O11 and NiMoO4-doped Bi2Ti4O11, the starting materials taken were Bi (NO3)3, Ni (NO3)2, (NH4)2MoO4, and Ti-tartarate, triethanolamine (TEA).

The titanium tartarate solution was prepared by the following procedure. TiO2 powder is dissolved in 40% HF solution

Characterization of the prepared powders

The XRD patterns of the prepared samples of Bi2Ti4O11 and NMxBT1−x (x = 0.01) composite are shown in Fig. 2 in which the XRD pattern of NiMoO4-doped Bi2Ti4O11 alloy exactly matched with the XRD pattern of undoped Bi2Ti4O11 due to solubility of NiMoO4 in Bi2Ti4O11. The XRD shown in Fig. 3 provides the effects of calcinations temperature on the crystallization of 1 mol% NiMoO4-doped bismuth titanate composite. As shown in the figure, the prepared samples have been well crystallized when calcined

Conclusions

Nano-sized NiMoO4-doped Bi2Ti4O11 composite were synthesized by a CSD method. Photocatalytic activities of the prepared samples have been evaluated by the photodegradation of methyl orange solution under Hg-lamp. NMxBT1−x (x = 0.01) photocatalysts is most photoactive for decolorization of methyl orange compared to, pure NiMoO4, pure Bi2Ti4O11 and other doped composition except P25 titania. A mechanistic scheme for photocatalytic activity is presented suggesting the high-photocatalytic activity

Acknowledgements

Authors thank P.V. Satyam, IOP, Bhubaneshwar, India for their assistance in the HRTEM work. Authors also thank Council of Scientific and Industrial Research for financial support.

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