A systematic review of photocatalytic degradation of humic acid in aqueous solution using nanoparticles

Abstract

Objectives Humic acid (HA) compounds in the disinfection processes of drinking water and wastewater are considered as precursors of highly toxic, carcinogenic and mutagenic disinfectant by-products. The aim of this study was to systematically review all research studies on the photocatalytic degradation of humic acid and to evaluate the laboratory conditions and results of these studies. Content The present systematic review was performed by searching the Scopus, PubMed, and web of science databases until December 2021. The parameters of type of catalyst, catalyst size, optimum pH, optimum initial concentration of humic Acid, optimum catalyst concentration, optimum time, light used and removal efficiency were investigated. Summary 395 studies were screened and using the inclusion and exclusion criteria, in total, 20 studies met our inclusion criteria and provided the information necessary to Photocatalytic degradation of humic acid by nanoparticles. In the investigated studies, the percentage of photocatalytic degradation of humic acid by nanoparticles was reported to be above 70%, and in some studies, the removal efficiency had reached 100%. Outlook From the results of this systematic review, it was concluded that the photocatalytic process using nanoparticles has a high effect on the degradation of humic acid.

Perspectives for Photocatalytic Decomposition of Environmental Pollutants and Pathogens on Photoactive Particles of Soil Minerals

“…The chemistry of processes leading to the formation of toxic derivatives of HA has been previously extensively studied, and described in the basic works on radical chemistry of aromatic compounds [170][171][172]. HA are poly-aromatic compounds that have a variety of components including quinone, phenol, catechol, and sugar moieties [173,174], with significant antioxidant properties and the ability to scavenge free radicals [174][175][176][177][178][179][180][181][182][183][184][185][186][187][188][189][190][191][192][193].…”

“…Additionally, quantum efficiency of photocatalysis can be reduced due to absorption of light by organic compounds, when the light-quantum has too low energy to cause dissociation of chemical bonds, and its absorption causes the solution to only heat up [194]. The fact that humic acids scavenge • OH radicals and its precursor VB h  , desired when photocatalysis is used for degradation of humic acids, causes a decrease in the effectiveness of photocatalysis when its purpose is to degrade other pollutants [181]. A large contribution has been made to improve the quality of drinking water, thanks to the development of organic matter removal methods [195][196][197][198][199][200].…”