Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-019-01517-4 Valorization of tire wastes to carbon quantum dots (P‑CDs) and photocatalytic degradation enhancement of organic wastes using ZnO‑CDs nanocomposites Nian N. Mohammad 1  · Khalid M. Omer 1  · Shirwan Baban 2 Received: 25 January 2019 / Accepted: 15 May 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Valorization of solid wastes for the production of valuable materials is of great importance for sustainable development. In this paper, removal for solid and liquid wastes via hydrothermal and catalytic degradation was reported. The frst removal process is the hydrothermal conversion of solid waste, here solid wastes of tire, to phosphorous and nitrogen doped carbon nanodots (P-CDs). The second removal is the visible-NIR light driven photocatalytic degradation of liquid waste, here methylene blue (MB) solution, using P-CDs loaded on ZnO nanoparticles. Energy-efcient light emitting diode (LED) was used as a weak sufcient irradiation source. Photodegradation rate constants for ZnO-P-CDs were almost 10 times higher (0.08 h −1 for ZnO-P-CDs) comparing to pure ZnO (0.008 h −1 ), such enhancement is signifcant for a weak light source. Cyclic voltammetry and optical properties were used to fnd HOMO and LUMO of P-CDs. Based on the energy levels of ZnO and P-CDs, the catalytic enhancement was attributed to increasing the separation rate of photogenerated electrons and hole due to the transfer of electrons from the conduction bands of P-CDs to the conduction band of ZnO. Up-conversion photoluminescence of P-CDs is another reason for increasing the separation of excitons and harvesting the longer wavelength light. The proposed approach, solid and liquid waste removal via hydrothermal and catalytic degradation combined with weak LED light, would be a powerful approach in solid waste treatment and water purifcation technology, simultaneously. 1 Introduction Recently, Mankind is facing water pollution and solid waste problems, especially in developing countries. It is well-rec- ognized that enormous quantities of waste materials still end up in landflls. A huge number of techniques is reported for water purifcation and solid waste treatment [1]. Currently, the tendency is to move towards new products of high value derived from the generated waste ofering new opportuni- ties at technological level to address modern societies. From here, one of the challenges is valorization of organic and industrial wastes for the production of the valuable chemi- cals [2, 3]. Waste valorization is the process of converting waste or biomass materials into more valuable products including chemicals, materials, and fuels [4, 5]. Due to tremendous increasing of vehicles, tire wastes are becoming environmental problems all over the globe. However, tire disposal is mostly through incineration, which emits a huge amount of toxic gases to the environment, such as; hydrocarbons, chlorinated gases, polychlorinated biphe- nyls (PCBs) [6]. Thus, one has to think about reusing and converting the solid wastes to useful products. On the other hand, advanced oxidation processes (AOPs) have been shown a promising environmentally friendly and facile methods to remove organic waste. Photocatalysis, as one of the AOPs, using various semiconductors is emerg- ing as an efcient technique for removing of many organic pollutants in polluted water and air [7]. After the frst report by Fuijishima and Honda for photocatalytic degradation of pollutants by TiO 2 to purify water [8], since then, the AOPs have been widely investigated suing diferent irradiation Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10854-019-01517-4) contains supplementary material, which is available to authorized users. * Khalid M. Omer khalid.omer@univsul.edu.iq 1 Department of Chemistry, College of Science, University of Sulaimani, Kirkuk Street, Sulaimani, Kurdistan Region 46002, Iraq 2 Gasha Technical Institute, GTI, Hasarok St., Erbil, Kurdistan Region, Iraq