Achieving tunable photocatalytic activity enhancement by elaborately engineering composition-adjustable polynary heterojunctions photocatalysts

• Composition-adjustable polynary heterojunction photocatalysts are fabricated.
• The as-obtained samples are divided into three classes with different components.
• The composite photocatalysts exhibit strong absorption in visible region.
• The composites show superior photocatalytic activity against diverse pollutants.
• The three classes photocatalysts show three types of photocatalytic mechanisms.

We first achieve controllable synthesis of composition-adjustable polynary heterojunction photocatalysts via a facile in-situ treatment strategy at ambient conditions based on component transformation and chemical deposition. By controlling the chemical reaction degree, three-classes of heterojunction composites with diverse components were produced. The first group (G1) contains AgI/AgIO3 two phases. The second group (G2) consists of Bi7O9I3/AgI/AgIO3 three phases. While the last group (G3) is composed of Bi7O9I3/AgI. Along with different phase constitution, it is very intriguing to observe that photoabsorption edges of the composites can be orderly tuned from 400 nm to 650 nm, covering almost the whole visible light region, consistent with the color change of samples from white to light yellow, orange and brick red. The three series of composite photocatalysts all show greatly enhanced photocatalytic activity in photodegrading methyl orange (MO) and NO gas removal under simulated solar light or visible light irradiation compared with the AgIO3 precursor. Among them, the intense photoabsorption and desirable band alignment (three-rank heterojunction) are well balanced in Bi7O9I3/AgI/AgIO3, thus showing the optimal photoreactivity, approximately 128 times than that of AgIO3. Particularly, it also exhibits unsurpassed photocatalytic performance against diverse industrial pollutants and pharmaceutical, such as Rhodamine B, phenol, 2,4-dichlorophenol, bisphenol A, and tetracycline hydrochloride. Additionally, three types of photocatalytic mechanisms corresponding to the three series of photocatalysts are systematically investigated and illustrated. It is found that different phase composition has a huge impact on the separation and migration of charges as well as active species. The present work not only provides new perspective into manipulating component-adjustable heterojunctional photocatalysts, but also opens an alternative avenue for developing composite materials for solar-conversion applications.

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