Understanding the influence of additives on methyl orange degradation using adsorption/photocatalysis functioned materials

Dye wastewater has a severe influence on natural water environment. Using materials functioned by adsorption and/or photocatalysis to degrade dyes has received much attention due to high decolorization efficiency. However, there are a very limited knowledge on how co-existing additives influence dye degradation using the adsorption and/or photocatalysis materials. In this context, this study selected biochar-TiO2 composites to test whether different additives (anions, surfactants, thickeners and heavy metals) can affect the dye decolorization efficiency. The biochar-TiO2 composites, dye solution and selected additives were poured into a series of quartz tubes, which were put in a photochemical reactor equipped with a mercury lamp to simulate ultraviolet radiation. The outcomes showed that the biochar-TiO2 composites had a strong capacity of degrading eight dyes with different characteristics and structures. After 1-hour dark adsorption, the decolorization efficiency of the eight dyes were 40 %–99.89 % while after 1-hour photocatalytic reaction, the decolorization efficiency all reached nearly 100 %. In addition, taking methyl orange (MO) as a case study, it is found that the presence of different additive types had different influences on MO degradation via positively/negatively affecting dark adsorption and/or photocatalytic reaction. The influence mechanisms of different additives were also explored such as occupying adsorption sites (negative influence) and stimulating the creation of ·OH (positive influence). The research outcomes are expected to contribute the useful knowledge to effective dye wastewater treatment.