Figure. 17.4. Synthetic approaches of g-C3N4 including (a) solid-state reaction, (b) electrochemical

deposition, (c) solvothermal reaction and (d) thermal decomposition.

Figure 17.4. Synthetic approaches of g-C3N4 including (a) solid-state reaction, (b) electrochemical deposition,

(c) solvothermal reaction and (d) thermal decomposition.

Modification Strategies of g-C3N4 for Potential Applications in Photocatalysis 297

17.4.1 g-C3N4 Modifications by Constructing Heterojunctions

By promoting the charge carrier’s separation and lowering e^–-h⁺ hole recombination, various metal

oxides, including tin oxide, zinc oxide, iron oxide, etc., can increase the photocatalytic activity

of g-C3N4. As a result, modified g-C3N4 nanocomposites have improved electric, magnetic and

photocatalytic properties and apply to a wide range of applications

such as CO2 reduction H2

generation, degradation of organic and inorganic dyes, NO oxidation and sensing, etc. (Chen et al.

2020, Rabani et al. 2021).

A few g-C3N4 heterojunction topologies based on metal oxides to g-C3N4 are compared here.

For g-C3N4-metal oxide photocatalysts, charge carrier separation can take five different forms:

i. Type I heterojunction

ii. Type II heterojunction

iii. Z-scheme heterojunction

iv. p-n heterojunction

v. Schottky junction

Most of g-C3N4 metal oxide photocatalysts exhibit type II and Z-scheme charge carrier separation

processes. Here these two types of heterojunctions will be discussed. “In type II heterojunctions,

two semiconductors are bonded together to produce stable heterojunctions.” The semiconductor

A’s valence band (VB) is positioned higher than semiconductor B’s. The photoinduced hole, in this

instance, traveled from the VB of semiconductor B to semiconductor A because of the disparity

in voltages (Figure 17.5a). On the opposite side, electrons are moved from semiconductor B’s

conduction band (CB) to semiconductor A’s. The improved separation of the electrons and holes