## 1 Introduction  
The industrial contamination of water, soil, or air, has always been an alarming issue for the human beings and life on Earth [1, 2, 3, 4]. One vital constituent that severely affects the earth lifecycle is use of unhygigenic and contaminated water due to industrial effluents and pollution. Hence, surrounded by industrialization and farming leftover, the major cause of organic impurities in water can be ascribed to the disposal of industrial wastewater without proper treatment. Amongst industries, the textile industry contributes to a great extent to water contamination and pollution, specifically in developing or underdeveloped countries [3; 5; 6]. The toxins present in textile wastewater consist of unmanageable toxic-colored dyes, surfactants, along with many chlorine-containing amalgams [3; 5; 7]. These dyes have the ability to persist in the environment for a prolonged time. The textile industry employs a variety of dyes which mainly consists of azo compounds, anthraquinones, diarylmethananes, phthalocyanines, etc. As reported approximately 70% of industrial wastewater consists of azo dyes [7]. These azo dyes are cancer-causing and also mutagenic in nature. They come into the body through incorporation as well as processing via gastric microbes and harming human and animal life. Recent investigations have paid attention to numerous wastewater treatment procedures such as biodegradation, coagulation, adsorption, chemical treatment, advanced oxidation processes (AOPs), and membrane processes [8]. Amongst the abovementioned approaches, AOP seems one of the favorable methods for degradation of organic dyes as it is a cost-effective, easy, and competent approach with the ability to degrade dye compounds into CO\({}_{2}\), water and other less hazardous intermediates. Amongst the various AOPs, photocatalysis is considered as a viable, renewable and eco-friendly approach for wastewater treatment [9; 10; 11; 12]. Photocatalysis employs a photocatalyst, generally a semiconductor material, and light for the treatment of organic compounds in wastewater. Under light irradiation, photo-excited charges are generated which initiate electrochemical reactions with wastewater on their surface and decompose the organic contaminants completely or partially into harmless intermediates. Amongst the variety of photocatalysts being investigated, titanium dioxide (TiO\({}_{2}\)) is still a widely used photocatalyst because of its abundance, cost effectiveness and excellent properties such as nontoxicity, high excitation binding energy, and photocatalytic active crystal phases (anatase, rutile and brookite) [13; 14; 15; 16]. Despite of all these benefits, TiO\({}_{2}\) has some major drawbacks including its limited optical absorption, i.e., limited light absorption due to a wide band gap (3.2 eV), and moderate recombination of photo-excited charge carriers (e\({}^{-}\)/h\({}^{+}\)), influencing its photocatalytic performance. Hence, to improve the photocatalytic performance of TiO\({}_{2}\), several strategies have been employed with the objective of narrowing down the band gap of TiO\({}_{2}\) which include methods such as metal and non-metals doping [17], noble metal loading [18; 19], hetero-junction structures [16; 20; 21; 22; 23; 24] and TiO\({}_{2}\)-based composites [20; 23; 25; 26]. Doping/co-doping with non-metals e.g., nitrogen, sulphur, carbon, fluorine, etc. in TiO\({}_{2}\) framework, are economical and capable of narrowing down the band gap leading to efficient photocatalyst behavior due to the resulting enhanced optical absorption [27; 28]. Amongst the various doped TiO\({}_{2}\) materials, nitrogen-doped TiO\({}_{2}\) (N-TiO\({}_{2}\)) have received wider attention for various applications. In N-TiO\({}_{2}\), nitrogen impurities are incorporated into the TiO\({}_{2}\) lattice, influencing mainly the optical properties via generation of new states leading to enhanced photocatalytic performance [29; 30].