Selectivity Enhancement in Heterogeneous Photocatalytic Transformations

Abstract

Photocatalysis has been invariably considered as an unselective process (especially in water) for a fairly long period of time, and the investigation on selective photocatalysis has been largely neglected. In recent years, the field of selective photocatalysis is developing rapidly and now extended to several newer applications. This review focuses on the overall strategies which can improve the selectivity of photocatalysis encompassing a wide variety of photocatalysts, and modifications thereof, as well as the related vital processes of industrial significance such as reduction and oxidation of organics, inorganics, and CO transformation. Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations. In addition, nonsemiconductor type photocatalysts, such as Ti-Si molecular sieves and carbon quantum dots (CQDs), are also briefly appraised in view of their special role in special selective photocatalysis, namely epoxidation reactions, among others. In the end, a summary and outlook on the challenges and future directions in the research field are included in the comprehensive review.

Brookite: Nothing New under the Sun?

“…In-depth studies concerning different band gap and trap states, face reactivity, the effects of crystal morphology and dimension, the presence of vacancies, and the generation of adsorbates and radicals are of great interest, and recently great progress has been made in the study of these properties. Photo-induced heterogeneous electron transfer (ET) across the semiconductor and adsorbed molecules, leading to the formation of radicals (e.g., •OH) is of particular relevance for any photocatalytic reaction, but studying such highly reactive species is challenging [91,99]. An emerging approach is based on the use of organic dye probes in microscopic fluorescence imaging, for the sensitive detection of reactive oxygen species, their diffusion in solution or air, and the identification of photocatalytic active facets on semiconductor surfaces [100,101].…”

“…The selectivity of photocatalytic systems can be enhanced by two main strategies: modification of the photocatalyst and optimization of reaction conditions (e.g., aeration, type of solvent, concentration and type of anions [90], use of membranes) [91]. Not surprisingly, the TiO 2 phase composition was demonstrated to have an effect on the selectivity of many photocatalytic reactions, such as ammonia oxidation [92], photoinduced decomposition of acetone, oxygenate photoreforming [6], and selective oxidation of alcohols to aldehydes [91,93]. For instance, the product distribution of ammonia oxidation was different in the case of rutile, yielding nitrates as a major product, and of anatase and brookite, yielding mild-oxidation products such as nitrites and N 2 [92].…”

Light‐Activated Rapid Disinfection by Accelerated Charge Transfer in Red Phosphorus/ZnO Heterointerface

“…In heterostructures, photoexcited charge carriers are transported not only along the surface of each component, but also at the interface . Notably, the effective transport of photoexcited charge carriers at the heterostructure interface plays a prominent role in improving the photocatalytic activity .…”

CQD-Based Composites as Visible-Light Active Photocatalysts for Purification of Water

“…This relatively new material has attracted huge interest in many fields including, but not limited to, electrocatalysis [6], biosensing [7][8][9][10], bioimaging [11][12][13][14], chemical sensing [15], and nanomedicine [16], due to their unique tunable photoluminescence (PL) properties, chemical inertness, high water solubility, ease and low cost of fabrication and, more importantly, low toxicity. Additionally, CQDs have also attracted considerable interest in various photocatalytic applications-environmental remediation [17][18][19][20][21], water splitting to produce H 2 production [22][23][24][25][26][27], CO 2 conversion [28][29][30], and synthesis of chemicals [28][29][30][31][32][33]-because when coupled with a semiconductor photocatalyst, CQDs can provide with several advantages, including improved light harvesting ability, efficient usage of the full spectrum of sunlight, efficient charge carrier separation, stability, and hinder charge recombination. Figure 1 illustrates the various applications of CQDs in photocatalysis (left) and their competitive optical and structural properties during each photocatalytic procedure (right).…”