Synthesis and characterization of TiO2 loaded cashew nut shell activated carbon and photocatalytic activity on BG and MB dyes under sunlight radiation

https://doi.org/10.1016/j.saa.2014.11.087Get rights and content

Highlights

  • TiO2 supported on CNSAC exhibits porous morphology.

  • In the synthesized composite catalyst, TiO2 exists in anatase phase.

  • Average crystallite size of TiO2 reduces upon loading on CNSAC.

  • Reduction in crystallite size gives rise to more photoexcitation and adsorption sites.

Abstract

Synthesis of titanium dioxide (TiO2) nanoparticles and TiO2 loaded cashew nut shell activated carbon (TiO2/CNSAC) had been undertaken using sol–gel method and their application in BG and MB dyes removal under sunlight radiation has been investigated. The synthesized photocatalysts were characterized by X-ray diffraction analysis (XRD), Fourier infra-red spectroscopy (FT-IR), UV–Vis-diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The various experimental parameters like amount of catalyst, contact time for efficient dyes degradation of BG and MB were concerned in this study. Activity measurements performed under solar irradiation has shown good results for the photodegradation of BG and MB in aqueous solution. It was concluded that the higher photocatalytic activity in TiO2/CNSAC was due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst. The kinetic data were also described by the pseudo-first-order and pseudo-second-order kinetic models.

Introduction

In recent years, there has been a magnificent amount of research and development in the area of photocatalytic degradation and heterogeneous photocatalysis [1], [2], [3], [4]. Various semiconductors such as CdS, ZnO, and TiO2 [5], [6], [7] have been used as photocatalysts due to their good photoactivity, high chemical stability, lower cost and being non-toxic and relatively inexpensive. Titanium dioxide (TiO2) has been widely used for water and air purification since many environmental pollutants can be degraded by decomposition and oxidation process on its surface [8], [9], [10]. Titanium dioxide (TiO2) has advantages over other photocatalysts, such as high activity, good stability, low cost and harmless to humans. However, the main drawback of TiO2 is its relatively large band-gap (anatase: 3.2 eV; rutile: 3.0 eV). As a consequence, TiO2 shows photocatalytic activity only to a small fraction (<5%) of incident solar irradiation [11]. Among those, anatase is the more photoactive, which is improved by its high crystallinity and large surface area [12]. Recently, an intense effort has been devoted to loading TiO2 on different supports such as TiO2/SiO2, TiO2/Zeolite, and TiO2/AC [13], [14], [15]. TiO2 supported on porous activated carbon increases its adsorption capacity of organic compounds [16], [17]. Activated carbon which is sometimes called activated charcoal or active carbon is used mostly in industry for its large adsorption capacity, fast adsorption kinetic and relative ease of regeneration [18].

Activated carbon can be synthesized from carbonaceous agricultural wastes such as coconut shell [19], bamboo [20], vegetable fibre [21] and acorn shell [22]. It is widely used as adsorbent as it possesses large surface area. Activated carbon has been suggested as an effective support for TiO2 in the removal of the pollutants [23]. In this study, activated carbon synthesized from cashew nut shell by chemical activation was used as the support for TiO2. Sol–gel method was used to prepare a TiO2 photocatalyst and TiO2 supported on activated carbon. The photocatalytic degradation of aqueous solution of Brilliant green (BG) and Methylene blue (MB) using TiO2 and TiO2 loaded CNSAC under sunlight radiation has been investigated and the adsorption kinetics of photocatalysis was also studied.

Section snippets

Preparation of cashew nut shell activated carbon

The cashew nut shells (CNS) were collected from Panruti taluk, Cuddalore district, Tamilnadu, India. The CNS was first washed with deionized water to ensure that all impurities were removed and then dried in an oven at 110 °C for 24 h. CNS was then ground and sieved to obtain precursors of particle size less than 2 mm. The precursors were impregnated in potassium hydroxide (KOH) solution at an impregnation ratio of 1:1 (wt.% ratio of KOH:CNS) and the mix was continuously stirred using a magnetic

X-ray diffraction (XRD) analysis

X-ray diffraction (XRD) patterns of CNSAC, TiO2 and TiO2/CNSAC catalysts are shown in Fig. 1a–c. The X-ray diffraction pattern of CNSAC (Fig. 1a) shows a broad hump revealing a predominantly amorphous structure, a typical characteristic of CNSAC. The pattern for TiO2 shows the diffraction peaks at 2θ values of 25.34°, 37.75°, 47.96°, 53.82°, 54.9°, 62.6°, 68.7°, 70.33° and 75.08°. They are assigned to (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 1 1), (2 0 4), (1 1 6), (2 2 0) and (2 1 5) reflections of anatase phase

Conclusions

TiO2 and TiO2/CNSAC were successfully synthesized by sol–gel method at room temperature and were characterized by XRD, FT-IR, UV-DRS and SEM with EDX. XRD study revealed that the TiO2 was present in anatase phase and average crystallite size got decreased when supported on activated carbon. Presence of surface functional groups responsible for interactions with photogenerated holes were confirmed using FT-IR. Spherical morphology of TiO2 and porous nature of composite catalyst was inferred from

Acknowledgements

The authors wish to thank Dr. S. Barathan, The Professor and Head, Department of Physics, Annamalai University, for having provided the necessary laboratory facilities to carry out this work. The authors also thank Centralized Instrumentation and Services Laboratory (CISL), Annamalai University and Sophisticated Analytical Instrumentation Facility (SAIF), Cochin, for providing their analytical instrument facilities.

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