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1. Introduction

The increase in pollution due to urbanization and industrialization has become a significant challenge for the sustainability of human society. The waste generated in different industries during crude oil storage, transportation, and refinery has become a global problem [1,2]. The water and soil pollution caused by several pollutants’ discharge is a critical public health concern due to their toxicity. These pollutants can cause many health effects such as neurological toxicity, lung cancer, lethargy, fatigue, depression, headaches, nausea, dizziness, throat and eye irritation, and acute and chronic respiratory effects [3]. Toluene, benzene, xylene, ethyl benzene, and phenolic compounds some of the main compounds categorized as pollutants posing severe threats to our environment [4,5,6]. In the present situation, environmental pollution has increased several-fold due to the mismanagement of industrial waste. This can negatively affect the ecosystem and make lands unusable for agriculture and many other purposes [7]. Therefore, it is essential to remediate these toxic pollutants in our environment [8,9,10].

To eliminate organic pollutants from the environment, numerous technologies have recently been established for their degradation. Organic pollutants can be degraded by different methods, such as physical, chemical, biological treatments and advanced oxidation techniques [9,11,12,13,14,15]. Organic pollutant photodegradation is an attractive “green” chemical technology to control pollution, where photocatalysis is the most widely and potentially applied method used for demineralization and degradation of such pollutants [16,17].

Various light sources have been applied for the excitation of heterogeneous catalysts [18], but the photodegradation approach is more economical if sunlight can be used compared to ultraviolet light [16,19,20]. The evolution of the term “photocatalysis” shows the development of certain fundamental concepts of photochemistry. The point where photochemistry became a discipline was when it became differentiated from thermal chemistry. Indeed, several researchers saw irradiation as one of the many methods available to catalyze a response that makes it quicker by, for example, heating or processing it with certain chemicals until the beginning of the 20th century [21]. Ciamician, the first scientist to systematically understand the chemical effect of light, took great pains in finding out if he had “initiated heat” alone rather than “light” [22]. This was appropriately allotted the term “photochemical,” whilst the word “photocatalytic” applied to reactions caused by light, but with the same result as thermal reactions. Another step further was the identification of electronically excited states, which became a general idea in 1914 and were part of Bodenstein’s photochemical reactions along with reactivity and thermodynamics. In an early stage, more distinction was made in the thermochemistry of the process itself. This allowed for photosynthesis to occur when part of photon energy in the products rose [22,23].

Around 43% of visible-light energy is solar, so visible-light catalysts are chosen in photoelectrocatalysis and photocatalysis processes. Until now, several semiconductive products have been utilized, including metal oxides (Ag₂O, TiO₂, Cu₂O, ZnO, Fe₂O₃, Ta₂O₅), metal selenides (CdSe and MOSe₂), metal phosphides (Ni₂P), metal sulfides (Bi₂S₃, ZnS, MoS₂, and CdS), multi-structure oxides (Sr TiO₃WO), metal halides and oxyhalides (AgBr, BiOBr) and metal-free materials (SiC, Si and g-C₃N₄), [24,25,26,27,28]. Those with a bandgap (Eg) greater than 3 eV, e.g., SrTiO₃, TiO₂, ZnO, KTaO₃, ZnS, and SrTiO₃, are called wide-bandgap photocatalysts, whereas catalysts with an Eg of less than 4 eV, e.g., Si, SiC, Ag₂O, Bi₂WO₆, CdSe, InTaO₄, Ag₃VO₄, CoO, Fe₂O₃, Cu₂O, TaON, Ta₃N₅, CdS, Bi₂S₃, g-C₃N₄, and BiVO₄, are photocatalysts that react to visible light [25,29].

Heterogeneous catalysts play a vital role in environmental pollution control [30,31,32]. Powdered semiconductor photocatalysts are commonly used in various areas, such as carbon reduction [33], selective organic transformations, environmental remediation [34], and water splitting [35]. There has been, in numerous applications, a growing interest in the use of semiconductors as photocatalysts. In 2015, around 5500 documents about photocatalytic applications were published, indicating that interest in heterogeneous photocatalysis was enormous and highly important in diverse research fields. This number has recently grown to over 13,000. A country-specific view of the increase in the number of publications on “photocatalytic degradation” is listed in Table 1. No commercially accessible material can currently meet all application requirements, such as cost-effectiveness, stability, high visible-light quantum efficiency, and security [36]. For such tasks to be completed, a highly effective architecture and system for environmental remediation and energy supply are needed to examine new visible-light semiconductor materials.

The development of nanomaterials has progressed from the synthesis of single-particles to multicomponent assemblies or hierarchical structures, where two or more pre-synthesized nanomaterials are coupled to obtain multifunctionality. Such multicomponent assemblies are termed nanohybrids. The development and use of these nanohybrids requires interdisciplinary knowledge from the energy and environmental sectors, including the applications reported in references [37,38,39,40,41,42,43]. There are previously published review articles on some types and uses of nanohybrids, including gold-graphene oxide nanohybrids [39], organic/inorganic nanohybrids [44], polymer nanohybrids for oil recovery [45], nanohybrids of epoxy/polyamide with carbon nanotubes [46], protein-inorganic nanohybrids [47], gold-based inorganic nanohybrids [48] and polymer-inorganic supramolecular nanohybrids [49].

Graphene is the basic structure of all other carbon allotropes. It is well noted that the potential applications of graphene its derivatives are mainly driven by progressive production of different graphene materials such as graphene oxide (GO), reduced graphene oxide (rGO), functionalized graphene oxide (fGO), and functionalized reduced graphene oxide (frGO) with specific attention to precise applications and this is expected to continue for at least a couple of decades as promising applications and requirements are disclosed [50,51]. Various literature reports on the synthesis, modification and application of photocatalysts based on graphene for energy and environment solutions have already been published [52]. Graphene, graphene and its derivatives [53,54], graphene in photocatalysis [55], graphene doping [56], graphene and graphene oxide sponge [57], nitrogen-doped graphene [58], structure of graphene and its disorders [59], strain engineering of graphene [60], mechanics of graphene nanocomposites [61], chemical vapor deposition of graphene [62], functional modification of graphene/graphene oxide [63], graphene-based fibers [64], and graphene-based electrochemical micro-supercapacitors [65] are some of the subjects that have been reviewed.

Considering the stability, reactivity, reusability, and light-responsive effect of bismuth (Bi) it has been widely used as a photocatalyst. Several state-of-the-art review articles on topics including barium potassium bismuth oxide [66], bismuth-based composite oxides [67], bismuth ferrite nanoparticles [68], bismuth vanadate-based materials [69], bismuth tungstate photocatalysts [70], and bismuth oxyhalides [71] have been published. Annual numbers of publications on graphene photocatalysts in the last ten years are shown in Figure 1a. Similarly, bismuth-containing compounds are significant photocatalysts that react to visible light and fascinating research has been published in the field of bismuth photocatalysis over the last ten years (Figure 1b).

This review, therefore, summarizes and discusses recent Bi-graphene photocatalysts and their energy and environmental sector applications. The choice of bismuth with graphene is due to the vast available literature, as shown in Figure 1. Furthermore, most bismuth-based photocatalysts are stable, reusable, photoactive, cheaper, and more environmentally friendly that other alternatives. Besides, due to some shortcomings of the pristine photocatalysts, such as charge carrier recombination, slow migration of charge carriers, and low visible light absorption [72,73].

This entry is adapted from the peer-reviewed paper 10.3390/en14082281