Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener A novel photocatalytic system consists of Co(II) complex@ZnO exhibits potent antimicrobial activity and efficient solar-induced wastewater remediation Amr A. Essawy a,b, ⁎ , Amr M. Nassar a,c , Wael A.A. Arafa a,b a Chemistry Department, College of Science, Jouf University, P.O. Box 2014, Sakaka, Aljouf, Saudi Arabia b Chemistry Department, Faculty of Science, Fayoum University, 63514 Fayoum, Egypt c Chemistry Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, Egypt ARTICLE INFO Keywords: Cobalt complex ZnO Photosensitization Photoredox mediator Photocatalysis ABSTRACT Recently, cobalt complexes have been engaged in contemporary scientific prospects. Thus, this work presents the synthesis of novel cobalt(II) complex (Co 2 L) from Schiff base ligand, N,N'-bis-(5-methoxysalicylidene)-trans-(1,4- cyclohexylenediamine) (H 2 L) and investigates its synergistically catalytic characteristics along with ZnO pho- tocatalyst via synthesis of novel composite Co 2 L/ZnO. The as-synthesized substances were characterized using FT-IR, UV/vis., TGA, XRD, and TEM. Co 2 L shows impressive antimicrobial properties compared to a typical antibacterial and antifungal agents, tetracycline and amphotericin B, respectively. The results confirmed that, the loaded cobalt complex photosensitizes ZnO augmenting its solar response and acts as redox mediator re- vealing marvelous reduction of electrons and holes recombination. Compared with bare ZnO, Co 2 L/ZnO com- posite exhibited better photocatalytic degradation of methylene blue under solar-irradiation within degradation efficiency 97.7%. The developed composite provides integrity of the optical and structural characteristics. Moreover, it articulates new insights towards the synthesis of low cost, highly stable, and efficient photocatalyst for wastewater remediation. 1. Introduction Increased industrial development and the resultant environmental pollution received increased attention (Essawy et al., 2017). In textile and others industrialization, dyes are considered the major constituent reveals pollution when discharged to the environment especially aquatic life. The produced colored wastewaters could be subjected to various chemical interactions rising sever effects (Lam et al., 2017). One of the widely used dyes is methylene blue (MB). It is a blue cationic 1,4-thiazine dye in which the positive charge resonates on both ni- trogen and sulfur atoms (Wainwright et al., 2006). Developing a facile, cost effective, safe and sturdy alternatives to remediate wastewater is an environmentally pressing necessity. Upon using conventional techniques like coagulation, adsorption, floccula- tion, ultrafiltration and reverse osmosis in the treatment of dye en- riched wastewater, pollutants are conveyed from one form to another rather than their destruction (Ahmed et al., 2017). Advanced oxidation processes (AOPs) and especially photocatalysis is promising in organic pollutants mineralization. The semiconductor ZnO is vastly used in photocatalysis in the disinfection and detoxification of the environment due to its special physicochemical properties (Larbi et al., 2017). However, its large exciton binding energy (60 meV) and the wide band gap (3.37 eV) delimits the response to visible portion of solar radiation highlighting an important challenge (Shi-qian et al., 2014). Another challenge to be dealt with is the fast recombination of photo-generated electron–hole pairs. Therefore, many reports were presented to enlarge the sensitivity of ZnO towards visible portion of solar spectrum and reduce the rate of electron/hole recombination. An impressive ap- proach approved that the doping of ZnO with Nobel metals (Au, Pt, Ag), Fe or N enhance the absorption of visible radiation from solar light. As well, this ameliorates the separation of hole-electron pair resulting in higher photodegradation activity (Vaiano et al., 2015; Dhiman et al., 2017; Essawy, 2018). Lately, complexes comprising cobalt have been engaged in con- temporary scientific research. These developed architectures are viable in dye-sensitized solar cells as they absorb the visible portion of sun- light within controlled redox characteristics (Yum et al., 2012). More- over, cobalt complexes are presented as efficacious catalysts in the generation of hydrogen gas via an electrochemical and photochemical reactions (Huo and Zeng, 2016; Song et al., 2017). Recent work reports https://doi.org/10.1016/j.solener.2018.05.073 Received 19 December 2017; Received in revised form 8 May 2018; Accepted 21 May 2018 ⁎ Corresponding author at: Chemistry Department, Faculty of Science, Fayoum University, 63514 Fayoum, Egypt. E-mail address: aae01@fayoum.edu.eg (A.A. Essawy). Solar Energy 170 (2018) 388–397 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T