Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-019-03959-8 RESEARCH ARTICLE - CHEMICAL ENGINEERING Synthesis of 3D Hierarchical Flower-like MgO Microstructure: Investigation of its Adsorption and Antibacterial Properties Pınar Karacabey 1 · Sude Döven 1 · Deniz Uzuno ˘ glu 1 · Ayla Özer 1 Received: 14 January 2019 / Accepted: 27 May 2019 © King Fahd University of Petroleum & Minerals 2019 Abstract The present study was carried out to assess the dye adsorption ability and the antibacterial activity of 3D hierarchical flower- like MgO microstructure (HFl-MgO), which was synthesized by chemical precipitation method. As-prepared material was characterized by SEM, EDX, XRD, and FT-IR. Response surface methodology was applied in order to understand and optimize the effect of the experimental parameters on the adsorption of Malachite Green (MG) dyestuff. A quadratic model was established as a functional relationship between four independent variables and the adsorbed dye amount at equilibrium. The equilibrium adsorbed dye amount was found as 8402.4867 mg/g at the optimum experimental conditions, which were the contact time of 150 min, temperature of 44.7980 °C, the adsorbent concentration of 0.50 g/L, and the initial dye concentration of 4648.2323 mg/L. The kinetic data fitted well to the pseudo-second-order kinetic model, both intraparticle and film diffusion were effective, and Freundlich model was suitable for the adsorption of MG onto HFl-MgO. The adsorption of MG onto HFl- MgO was spontaneous, increasing in the randomness of adsorbed species, and endothermic. The studied process proceeded through chemical adsorption in view of the calculated activation energy. It was observed that HFl-MgO could be used repeatedly as an efficient adsorbent for the color and COD removal of MG. Moreover, HFl-MgO had inhibitory effects on the growth of S. aureus, L. monocytogenes, and E. coli O157:H7. Keywords Adsorption · Antibacterial activity · Flower-like · Magnesium oxide · Malachite Green · 3D hierarchical microstructure 1 Introduction Various works for getting solutions to the treatment of water and wastewaters have been investigated because water pol- lution is a great important issue that human beings face [1]. Dyestuffs are being common as environmental pollutants in wastewaters, and they pose also a potential risk to human health and aquatic life [2]. Moreover, some water can be con- taminated by microorganisms that also causing human health problems. In this respect, in order to maintain the human health, to preserve the aquatic life, and to create an overall balance in the universe, it is important to apply economic, effective, and a non-toxic method for treating water and wastewaters contaminated by kinds of dyestuffs and microor- ganisms [3, 4]. In this regard, the adsorption of pollutants is B Deniz Uzuno ˘ glu denizuzunoglu4@gmail.com 1 Department of Chemical Engineering, Faculty of Engineering, Mersin University, Mersin 33343, Turkey an appropriate approach for both academic and industrial fields. Especially for dyestuff removal, one of the most fre- quently studied adsorbents is activated carbon; however, due to its high production and treatment cost, it is necessary to find alternative adsorbents with high adsorption capacity and low cost [2]. In recent years, porous hierarchically struc- tured oxide-based micro/nano-materials have attracted much attention in especially adsorption applications due to their outstanding physical and chemical properties. The porous hierarchical structures, such as snowflakes, tubes, multi- pods, flower-like, sheets, plate-like, windmills, sphere, and dendrites, have high specific surface areas, large surface-to- volume ratio, abundant active sites, and hierarchical channels for mass transfer/molecules storage. In these materials, a mesoporous framework connected in three dimensions can provide remarkable reactivity, allowing the adsorbate molecules to adsorb to the active centers occurred onto the framework surfaces [5]. Among the metal oxide micro/nano- materials, porous hierarchically structured magnesium oxide (MgO) structures are the most promising alkaline and inor- 123