The Challenges of Integrating the Principles of Green Chemistry and Green Engineering to Heterogeneous Photocatalysis to Treat Water and Produce Green H2

Abstract

Nowadays, heterogeneous photocatalysis for water treatment and hydrogen production are topics gaining interest for scientists and developers from different areas, such as environmental technology and material science. Most of the efforts and resources are devoted to the development of new photocatalyst materials, while the modeling and development of reaction systems allowing for upscaling the process to pilot or industrial scale are scarce. In this work, we present what is known on the upscaling of heterogeneous photocatalysis to purify water and to produce green H2. The types of reactors successfully used in water treatment plants are presented as study cases. The challenges of upscaling the photocatalysis process to produce green H2 are explored from the perspectives of (a) the adaptation of photoreactors, (b) the competitiveness of the process, and (c) safety. Throughout the text, Green Chemistry and Engineering Principles are described and discussed on how they are currently being applied to the heterogeneous photocatalysis process along with the challenges that are ahead. Lastly, the role of automation and high-throughput methods in the upscaling following the Green Principles is discussed.

t-BuOOH/TiO2 Photocatalytic System as a Convenient Peroxyl Radical Source at Room Temperature under Visible Light and Its Application for the CH-Peroxidation of Barbituric Acids

“…Room temperature (rt) stands for 23-25 • C. 1 H and 13 C NMR spectra were recorded on Bruker (Bruker AXS Handheld Inc., Kennewick, WA, USA) AVANCE II 300 and Bruker Fourier 300HD (300.13 and 75.47 MHz, respectively) spectrometers in CDCl 3 and DMSO-D 6 . Residual signals of CDCl 3 (7.26 in 1 H NMR, 77.16 in 13 C NMR) were used as reference signals for precise chemical shift determination.…”

“…(1,2-Bis(tert-butylperoxy)ethane-1,1-diyl)dibenzene 4 [95] was isolated via column chromatography (EtOAc/petroleum ether = 1/40, R f = 0.4) as a colorless liquid (30 mg, 8%). 1 H NMR (300 MHz, Chloroform-d) δ 7.43-7.37 (m, 4H), 7.36-7.27 (m, 6H), 4.84 (s, 2H), 1.24 (s, 9H), 1.12 (s, 9H). 13 2,6-Di-tert-butyl-4-(tert-butylperoxy)-4-methylcyclohexa-2,5-dien-1-one 7 was isolated via column chromatography (EtOAc/petroleum ether = 1/50, R f = 0.9) as yellow powder (43 mg, 14%).…”

“…Mp = 84-85 [53]. 1 H NMR (300 MHz, Chloroform-d) δ 6.93-6.87 (m, 2H), 6.76-6.70 (m, 2H), 3.73 (s, 3H), 3.21 (s, 2H), 3.12 (s, 6H), 1.22 (s, 9H). 13…”

“…Heterogeneous photocatalysis has recently gained a lot of attention as an ideal tool for green chemistry [1]. It utilizes the energy of light using non-toxic environmentally friendly photocatalysts that can be easily recycled and reused.…”

“…Titanium dioxide (TiO 2 ) is the most widely used heterogeneous photocatalyst due to its excellent chemical stability, low toxicity, moderate cost and availability [2]. The most profound applications of TiO 2 are currently solar cell design [3,4], the oxidative destruction of pollutants [1,[5][6][7], photodisinfection [8], hydrogen generation [9][10][11][12], CO 2 reduction [2,13] and water splitting [14]. One of the most important challenges for TiO 2 application in organic synthesis is to shift its activity form UV to visible light [15][16][17][18].…”