The management of plastics waste is one of the most urgent and significant global problems now. Historically, waste plastics have been predominantly discarded, mechanically recycled, or incinerated for energy production. However, these approaches typically relied on thermal processes like conventional pyrolysis, which are energy-intensive and unsustainable. In this Minireview, some of the latest advances and future trends in the chemical upcycling of waste plastics by photocatalytic, electro-lytic, and microwave-assisted pyrolysis processes are discussed as more environmentally friendly alternatives to conventional thermal reactions. We highlight how the transformation of different types of plastics waste by exploiting alternative energy sources can generate value-added products such as fuels (H 2 and other carbon-containing small molecules), chemical feedstocks, and newly functionalized polymers, which can contribute to a more sustainable and circular economy.
Glycerol is a significant byproduct
of biomass conversion into
biodiesel, and numerous studies have been focused on its valorization
technologies in recent years. Photocatalytic glycerol valorization
is a promising technology to convert solar energy into chemical energy
by producing hydrogen and value-added liquid products. This technology
is desirable from the point of view of both green chemistry and sustainable
development since it can operate at ambient temperature and atmospheric
pressure by using renewable solar energy. The key element for a successful
photocatalytic glycerol valorization process is the development of
highly active and stable photocatalysts. In this context, the present
review deals with novel techniques to improve photocatalysts’
activity. It reviews the main characteristics, preparation methods,
advantages, and drawbacks as well as the performance of different
TiO2-based and non-TiO2-based photocatalysts
for glycerol conversion. Also, an analysis is presented on the most
effective approaches for increasing the photocatalytic activity, including
cocatalyst deposition, doping with metallic and nonmetallic ions,
development of carbonaceous composites, and formation of heterojunctions.
The review also offers the readers ongoing challenges and opportunities
for research on photocatalyst development to selectively convert glycerol
into hydrogen and value-added liquid products.
Incorporation
of carbonaceous templates (CT) into TiO2 composites is
a promising alternative to increase the photocatalytic
activity of TiO2. In this work, the effects of carbon sphere
(CS) and carbon nanotube (CNT) incorporation (as CT) in TiO2 composites were thoroughly investigated and the roles of these CTs
as template, cocatalyst, and adsorbent were studied. To this end,
three different methods were utilized to form a layer of TiO2 on the CT: alcoholic phase sol–gel, aqueous phase sol–gel,
and hydrothermal. The role of CT as template was examined through
morphology analysis of the prepared composites. The cocatalyst and
adsorbent roles of CT were investigated based on photocatalytic hydrogen
production from glycerol.
Interestingly, it was found that the incorporation of CNT into TiO2 composite can approximately double the rate of hydrogen production
(i) in the absence of Pt or (ii) at low glycerol concentration. Accordingly,
it was concluded that in addition to being a template, the CNT can
play two important roles as cocatalyst and adsorbent.
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