With the development of increasing the world population and continuous industrial and agricultural development, more and more organic contaminants in water sources have been observed over the world. The water with a high concentration of organic contaminants could be treated with biological treatment processes, while the wastewater contains toxic pollutants with low biodegradability from several industries such as pharmaceutical, textile and agricultural. The most important is that these toxic chemicals had been ubiquitously discovered in surface water, ground water, and municipal sewage treatment plant. Since the effect of TiO2 photoelectrode was first reported by Fujishima and Honda, photocatalysis is one of the most advanced oxidation processes. Among them, ruthenium photocatalysis is an environmentally friendly, sustainable, and energy-saving technology that can be applied to low biodegradability, high complexity, and high concentration of pollutants in the wastewater.
Figure 1. The ruthenium element
Ruthenium photocatalysis is an environmentally, friendly, sustainable, and energy-saving technology and widely used in various fields, such as phototherapy, fluorescent probes, biological imaging, organic sensitizing dyes, organic photovoltaics and photosensitized reaction. Therefore, it is very necessary for us to understand the factors that affects ruthenium photocatalysis.
During the photocatalytic process, the amount of the ruthenium photocatalyst is significant in photodegradation. The total catalyst surface area is affected by photocatalyst dosage. It is noted that the larger surface area has more actives sites and a positive correlation between the photocatalyst dosage and the degradation rate. When the photocatalyst dosage is beyond its optimum amount, this relationship will be invalid and the reaction may be decelerated. The results suggest that inhibition of the light from penetrating depth into the solution owning to the agglomeration of the photocatalyst. Therefore, the clusters of the photocatalyst inhibited the light from irradiating on a large catalytic area and sequentially more light will be scattered off.
Figure 2. Ruthenium photosensitizers affect by photocatalyst dosage）
The initial substrate concentrations is one of the most important parameters in the photocatalytic process. Under the constant operating parameters, different initial substrate concentrations need different irradiation times to reach a same stage. Although there are so many reactive radicals (∙OH and∙O2−) at a low substrate concentration, the hydroxyl radicals located near to the surface of the solid catalyst only lasted for a few nanoseconds to microseconds. At the high substrate concentration, the chance of collision between the substrate and the respective sites is limited. Therefore, a suitable initial substrate concentration is important for photocatalytic process.
With the change of solution's pH, the characteristics of the surface charge on photocatalyst, the size formation of aggregates and the adsorption behavior of the compounds will be changed. The important is that with pH value increased, the amount of hydroxyl radicals in the solution is increased and sequentially enhances the removal efficiency of pollutants.
Figure 3. Ruthenium photosensitizers affect by initial pH
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