Polyaniline based binary nanocomposite heterostructures with semiconductor photocatalysts for photocatalytic improvement

• Nanocomposite, conducting polymer characteristics , and various synthesis approaches of polyaniline presented along with their merits and demerits. • Use of PANI in water remediation via different methods is discussed. • Various synthesis routes and procedures of PANI nanocomposites are shown. • Type-II, p-n, Z-scheme, and S-scheme heterojunction structures of PANI with numerous photocatalysts in binary nanocomposites are discussed. • Photocatalytic implications of PANI binary nanocomposite photocatalysts with various semiconducting materials are presented. • Photocatalytic mechanisms of PANI binary nanocomposites for ROS generation also included. Composites are multiphasic materials that show improved characteristics compared to the consisting components. In nanocomposites, the sizes of components fall in the nano dimension due to which they exhibit extraordinary features compared to normal composites and are explored in numerous areas efficiently. Polyaniline (PANI) is a fascinating conducting polymer (CP) that is extensively utilized in various fields including water remediation and generation of composites of various semiconductor photocatalysts for improvement of photocatalytic efficiency, stability, recovery and recyclability, and reduction of agglomeration and photoinduced dissolution in solution due to extensive delocalized pi-electron system, effective mobility of electrons, lower band gap, and presence of aromatic amine functionalities in the polymer backbone. PANI forms binary and multi-component nanocomposites with photocatalysts such as metal-based (metal, metal oxide, metal sulfide, metal halide, metal ferrites, etc.), and carbon-based (GO, rGO, g-C 3 N 4 , CNT) which exhibit highly improve photocatalytic performance compared to pristine semiconductor photocatalysts against numerous water pollutants. Usually, PANI in the binary nanocomposites with the metal- and carbon-based semiconductor photocatalysts generates heterojunction structures of type-II, p-n, Z-scheme, and S-scheme and reduces band gap, enhances optical absorbance in visible light, increases separation of charge carriers, and their delocalization and via this prevent charge carriers recombination and their life span due to which photocatalytic performance is amplified. This review study is planned to present a review on PANI based binary nanocomposite photocatalysts, their synthesis, features, and photocatalytic applications for degradation of organic pollutants (dyes, phenolic pollutants, nitroaromatics, pesticide, pharmaceuticals pesticides, etc.) and inorganic pollutants under visible, UV, and solar light exposure at numerous reaction conditions. Moreover, this study highlighted various synthesis procedures of polyaniline and their merits, and demerits, synthesis routes of polyaniline nanocomposites.