Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece Effect of carbon nanotubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst synthesized via a modified sol-gel method Hor-Yan Phin, Yit-Thai Ong ⁎ , Jin-Chung Sin Department of Petrochemical Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia ARTICLE INFO Keywords: Zinc oxide Carbon nanotubes Photocatalyst Modified sol-gel Photocatalytic activity ABSTRACT Environmental crisis caused by constantly discharged of anthropogenic pollutants into the water bodies has been increasingly arousing the concern of public. Semiconductor metallic oxide such as zinc oxide with photocatalytic ability can serve as an auspicious alternative in tackling the issues mentioned. Nevertheless, massive re- combination rate of photo-induced charge carriers, agglomeration and photocorrosion of zinc oxide often reduce its photocatalytic degradation performance. Therefore, this study aimed to elucidate the effect of carbon na- notubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst that synthesized via a modified sol-gel method whereby the synthesis pathway excludes the necessity for organic additive and subsequence annealing treatment. Besides, the carbon nanotubes were added and ultrasonicated with precursor prior to the formation of zinc oxide which can enable the carbon nanotubes to serve as nucleation sites for the growth of zinc oxide. The zinc oxide was found to be attached on carbon nanotubes surface through the for- mation of zinc carboxylate group and morphologies of the zinc oxide/carbon nanotubes photocatalyst showed that the aggregation of zinc oxide was reduced in the presence of carbon nanotubes. The band gap energy of zinc oxide photocatalyst was slightly blue shifted after hybridized with carbon nanotubes. The zinc oxide/carbon nanotubes photocatalyst demonstrated greater photocatalytic activity than pure zinc oxide in degrading me- thylene blue under irradiation of sunlight and the photocatalytic activity of the zinc oxide/carbon nanotubes photocatalyst was increased with increasing carbon nanotubes loading. An optimum photocatalytic activity was obtained using zinc oxide/carbon nanotubes with 10 wt.% carbon nanotubes. 1. Introduction Water scarcities, severe contamination of water and waterborne diseases have been consistently posing menace to the living ecosystem [1]. Notably, growing demand on clean water by burgeoning human population and constantly expelling anthropogenic pollutants in virtue of rapid industrialization have further exacerbated the water crisis [2,3]. Efficacious treatment for decontamination of polluted water source is imperative to tackle water resource dwindling and sanitation pertinent issues. Several technologies have been widely employed in treating dye laden industrial wastewater such as adsorption [4,5], precipitation [6], coagulation-flocculation [7], ozonation [8], biolo- gical methods [9], photocatalysis [10] and membrane filtration [11], respectively. Nonetheless, these treatments are ineffective in deconta- mination dyes containing effluent as these methods merely transferring the contaminants from one phase to another phase without further processing and thus eventuate in secondary pollution [12]. Advanced oxidation process (AOP) using heterogeneous semi- conductor photocatalyst has been viewed as a promising alternative in tackling the polluted water issue. The AOP involves generation of hy- droxyl radical which induces oxidation process to mineralize organic and inorganic pollutants in water [13]. Zinc Oxide (ZnO) semi- conductor has garnered immoderate advertence as its superb attributes make it an ideal candidate as photocatalyst. It has numerous ad- vantages included low cost, non-toxic nature, environmental friendli- ness, excellent chemical and mechanical stability [14]. Furthermore, ZnO exhibits greater photocatalytic activity than the titanium dioxide (TiO 2 ) particularly in degradation of dyes [15,16]. Nevertheless, high recombination rate of photo-generated charge carriers [14,17], prodi- gious agglomeration and reduced photostability with prolonged of ir- radiation under sunlight [18] limit its practicability in wastewater treatment. The high surface energy and diminished suspension https://doi.org/10.1016/j.jece.2019.103222 Received 17 January 2019; Received in revised form 17 April 2019; Accepted 19 June 2019 ⁎ Corresponding author. E-mail address: ongyt@utar.edu.my (Y.-T. Ong). Journal of Environmental Chemical Engineering xxx (xxxx) xxxx 2213-3437/ © 2019 Elsevier Ltd. All rights reserved. Please cite this article as: Hor-Yan Phin, Yit-Thai Ong and Jin-Chung Sin, Journal of Environmental Chemical Engineering, https://doi.org/10.1016/j.jece.2019.103222