Figure. 17.5. (a) type II heterojunction, (b) Z-scheme heterojunction

298

Bioremediation for Sustainable Environmental Cleanup

Figure 1 7 . 5. (a) Type II heterojunction, (b). Z-scheme heterojunction.

will lengthen the lifespan of the electrons and slow down recombination. Building type II systems

for photocatalysis in various applications is highly desirable.

The direct Z-scheme heterojunction was first proposed by (Bard and Fox 1995). The produced

electrons on the CB of semiconductor B move to the VB of semiconductor A, as illustrated in

Figure 17.5b, where they mix with the photogenerated holes. By increasing the separation of

electrons and holes, these photocatalysts can reduce recombination while enhancing redox

capability. Different electron and hole migration patterns are caused by the electric field’s driving

force, which is created by the band edge positions of various semiconductors. Charge carriers begin

to move in the electrical field direction to decrease the system’s energy. As a result, various systems

are identified based on electron and hole migration in the heterojunction. The flow of electrons and

holes is primarily responsible for the differences between each type of heterojunction.

17.4.2 g-C3N4 Modifications by Doping

17.4.2.1 Metal-based Doping

The use of g-C3N4 in wastewater remediation and water filtration has just evolved to a nascent

level. The application of noble metals (i.e., Pd, Ru, Ag, Au, Pt, Ir and Os) as dopants is a costly process

that has limited their use on a broad scale due to their rarity and corrosive character. Therefore,

it is crucial to design a metal-doped g-C3N4 based photocatalyst to produce real earth-abundant

photocatalytic systems for water and wastewater treatment. By reducing the band gap, improving

visible light absorption and increasing surface area, the addition of metals as dopants boosts the

photocatalytic capabilities of g-C3N4.

The most used synthesis method is thermal condensation, which involves mixing the

appropriate soluble metal salt with the g-C3N4 precursor in distilled water while ensuring a constant

heat source to achieve the goal of a modulated band gap (Jiang et al. 2017, Zhu et al. 2015). The

modification of g-C3N4 has also been done using this method. By employing ferric chloride as

the Fe-precursor (Tonda et al. 2014), synthesized Fe-Doped g-C3N4 nanosheets. To create a more

effective and recyclable photocatalyst for wastewater disinfection, several research groups have

synthesized metal-doped g-C3N4.

For extended visible-light photocatalysis, metallic impurities like Na⁺ and K⁺ were inserted

into the N sites of the g-C3N4, taking advantage of the improved electronic structures, adjustable