<p>The synthetic dye industry is a important driving force behind a diverse variety of fields, such as the textile, light, and chemical industries. In particular, the textile industry is a main consumer of these synthetic dyes - 10,000 tons out of the 7 × 107 tons of synthetic dyes produced worldwide are used by textile industries <ahref="https://doi.org/10.1016/j.ecoenv.2021.113160"><sup>[1]</sup></a>.</p>
<p>China is widely regarded as the “world's factory”, and the name holds true for its role in the dye and textile industries. In terms of annual production, export, and retail, China firmly holds first place in the world textile industry. The sector has experienced consistent economic growth over the last decade, now producing nearly 65% of the world’s clothing <ahref="https://doi.org/10.3390/textiles2010010"><sup>[5]</sup></a>. In the dye industry, its fuel production and trade volume rank first in the world (Xu et al., 2002).</p>
<p>China is widely regarded as the “world's factory”, and the name holds true for its role in the dye and textile industries. In terms of annual production, export, and retail, China firmly holds first place in the world textile industry. The sector has experienced consistent economic growth over the last decade, now producing nearly 65% of the world’s clothing <ahref="https://doi.org/10.3390/textiles2010010"><sup>[5]</sup></a>. In the dye industry, its fuel production and trade volume rank first in the world <ahref="https://doi.org/10.1016/j.jclepro.2019.03.307"><sup>[9]</sup></a>.</p>
<p>However, this economic prosperity has a dark side. The amount of waste water discharged by the textile industry is as high as 900 million tons per year, accounting for the sixth place in industrial discharge <ahref="http://dx.doi.org/10.1088/1755-1315/514/5/052001"><sup>[12]</sup></a>. Untreated textile wastewater contains a high concentration of toxic chemical dyes and heavy metals discharged as effluent, which contaminate local waters, causing serious pollution and posing a serious risk to aquatic ecosystems and human health.</p>
<p>Current treatment methods for industrial wastewater include physical methods, such as filtration, flocculation and adsorption; or chemical methods, like oxidation and ozonation. However, the water-soluble and stable properties of synthetic dyes make them difficult to be removed from wastewater using simple treatment methods <ahref="https://doi.org/10.1016/j.tca.2019.03.024"><sup>[11]</sup></a>, and the possible generation of toxic intermediates raises concerns on ecofriendliness. These methods also require expensive machinery and chemicals, which are unaffordable for many small scale factories and companies <ahref="https://doi.org/10.1016/j.jece.2020.105012"><sup>[11]</sup></a>.</p>
