Catalytic conversion of CO2 to produce fuels and chemicals is attractive in prospect because it provides an alternative to fossil feedstocks and the benefit of converting and cycling the greenhouse gas CO2 on a large scale. In today's technology, CO2 is converted into hydrocarbon fuels in Fischer-Tropsch synthesis via the water gas shift reaction, but processes for direct conversion of CO2 to fuels and chemicals such as methane, methanol, and C2+ hydrocarbons or syngas are still far from large-scale applications because of processing challenges that may be best addressed by the discovery of improved catalysts-those with enhanced activity, selectivity, and stability. Core-shell structured catalysts are a relatively new class of nanomaterials that allow a controlled integration of the functions of complementary materials with optimised compositions and morphologies. For CO2 conversion, core-shell catalysts can provide distinctive advantages by addressing challenges such as catalyst sintering and activity loss in CO2 reforming processes, insufficient product selectivity in thermocatalytic CO2 hydrogenation, and low efficiency and selectivity in photocatalytic and electrocatalytic CO2 hydrogenation. In the preceding decade, substantial progress has been made in the synthesis, characterization, and evaluation of core-shell catalysts for such potential applications. Nonetheless, challenges remain in the discovery of inexpensive, robust, regenerable catalysts in this class. This review provides an in-depth assessment of these materials for the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2 into synthesis gas and valuable hydrocarbons.

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Core–shell structured catalysts for thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2

Water is an essential part of life and its availability is important for all living creatures. On the other side, the world is suffering from a major problem of drinking water. There are several gases, microorganisms and other toxins (chemicals and heavy metals) added into water during rain, flowing water, etc. which is responsible for water pollution. This review article describes various applications of nanomaterial in removing different types of impurities from polluted water. There are various kinds of nanomaterials, which carried huge potential to treat polluted water (containing metal toxin substance, different organic and inorganic impurities) very effectively due to their unique properties like greater surface area, able to work at low concentration, etc. The nanostructured catalytic membranes, nanosorbents and nanophotocatalyst based approaches to remove pollutants from wastewater are eco-friendly and efficient, but they require more energy, more investment in order to purify the wastewater. There are many challenges and issues of wastewater treatment. Some precautions are also required to keep away from ecological and health issues. New modern equipment for wastewater treatment should be flexible, low cost and efficient for the commercialization purpose.

Role of Nanomaterials in the Treatment of Wastewater: A Review

UV-A: Biological Effects of Ultraviolet Radiation, with Emphasis on Human Responses to Longwave Ultraviolet. By J. A. Parrish, R. A. Anderson, F. Urbach and D. Pitts. Pp.262. (Plenum: New York and London, 1978.) £15.75.

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Biological effects of ultraviolet radiation

Fundamentals and photocatalysis of methylene blue dye using various nanocatalytic assemblies- a critical review

An overview of homogeneous and heterogeneous photocatalysis applications for the removal of pharmaceutical compounds from real or synthetic hospital wastewaters under lab or pilot scale

Photocatalytic reactor design for environmental applications is a major challenging task in heterogeneous photocatalysis because all the three components involved in the process are in different phases: pollutant - fluid, catalyst – solid and light photons - massless particles. Heterogeneity of photocatalysis makes the reactor design highly inter-disciplinary involving the knowledge of chemical, mechanical and environmental engineering concepts. So far literatures have focused on optimizing process parameters for specific pollutants, but the holistic approach in designing a photocatalytic reactor has been unclear. This article reviews about all types of photocatalytic reactors and compares them with calculated five benchmarks: Apparent reaction rate constant (k), Space time yield (STY), Photocatalytic space time yield (PSTY), Specific removal rate (SRR), Electrical energy consumption (EEC). It is interpreted that in designing a photocatalytic reactor, four important aspects are to be considered: Throughput, Performance, Energy efficiency, Cost. This review article calculates the above said 5 benchmarks for 24 reactor designs and highlights the important parameters to build an effective photocatalytic reactor.

Progression of Photocatalytic reactors and it's comparison: A Review

The main source of drinking water for rural communities in India is rainwater harvesting ponds. These ponds do have a sand filtration system for turbidity removal, but the bacteriological quality of these ponds is not under compliance in most cases. In this context, Pattikadu village in Kancheepuram District (Tamil Nadu, South India) was chosen as the study area. It was observed that the biological parameter of drinking water from hand pumps exceeds the limit prescribed by Indian standards. In this work, zero-energy disinfection technology was developed using UVC-LEDs for drinking water to meet the standards. The electrical power required for the disinfection was taken from the mechanical energy from up and down movement of the hand pump lever. UVC-LEDs (λemission 275± 5 nm) were powered by a 6 V rechargeable battery which stores electrical energy by mechanical movement of the hand pump lever. An annular-type UVC-LED photo-reactor (1 litre) was developed and 100% disinfection within 6 minutes’ contact time was achieved. The UVC dose-based inactivation rate constant was 0.57 cm/mJ. The present study demonstrated 2-log inactivation for a 4.68 mJ/cm UVC dose. The novelty of the study is its practical applicability of a sustainable point-ofuse disinfection technology which might be economically implemented in lower-income smaller communities.

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Design and evaluation of zero-energy UVC-LED reactor fitted with hand pump system for disinfection

The present study is an exhaustive comparison between three types of reactors for Acid Red 87 removal using graphene oxide under combined processes. Acid Red 87 or Eosin Y is brominated flu-orescein structure which forms a red fluorescence. From late 19th century, this dye was extensively used in textile industries. The degradation of this fluorescent dye is problematic due to its high molar mass and stability. The performance of three reactor types: (1) concentric cylindrical glass tube micro- reactor (CGTR), (2) UV-LED strip photocatalytic reactor and (3) classical annular reactor were evaluated for the Acid Red 87 removal. The maximum of 94.8% dye removal and 61.5% total organic carbon removal was achieved at initial pH 6, 2 g/L catalyst dosage and 44 mM H 2 O 2 concentration under 60 min in CGTR. Further comparative parameters were calculated and the best parameter values were obtained for CGTR in terms of performance and energy efficiency.

Comparative study on concentric cylindrical glass tube micro-reactor, UV-led strip photocatalytic reactor and classical annular reactor on Acid Red 87 removal

Seaweed Bioprocessing for Production of Biofuels and Biochemicals

The scalability of photocatalytic reactor is the major challenge due to the inability of the light penetration when the laboratory scale reactors are ascended. It is well known that the characteristic length of photocatalytic reactor is one of the influential parameters determining the efficiency of light penetration and also affects the hydrodynamic fluid flow behaviour inside the reactor. This study visualizes hydrodynamic flow behaviour of three differently configured photocatalytic reactors through numerical simulation of the fluid mass transport inside the reactors. The three photocatalytic reactors are (1) concentric cylindrical glass tube micro-reactor (CGTR), (2) UV-LED strip photocatalytic reactor (STR) and (3) classical annular reactor (CAR) from our previous work. The simulations of flow behaviour confirmed that CGTR exhibited plug flow regime, STR exhibited arbitrary flow (in-between continuously stirred tank reactor and plug flow reactor) and CAR behaved like continuously stirred tank reactor. Also, interpretations of numerical modelling were validated through plotting experimental residence time distribution curve. Furthermore, the comparison of performance parameters revealed that the highest modified space time yield (STYmodified) 225 s-1and highest modified photocatalytic space time yield (PSTYmodified) 9.375 s-1/kW/m3 was obtained for plug flow reactor when compared to continuously stirred tank reactor (CAR) and arbitrary flow reactor (STR). The study confirms that decrease in characteristic length of photocatalytic reactor onsets plug flow regime, which has highest photocatalytic performance efficiency. 

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Kaviya Piriyah Sundar

Papers

Progression of Photocatalytic reactors and it's comparison: A Review

Design and evaluation of zero-energy UVC-LED reactor fitted with hand pump system for disinfection

Comparative study on concentric cylindrical glass tube micro-reactor, UV-led strip photocatalytic reactor and classical annular reactor on Acid Red 87 removal

Seaweed Bioprocessing for Production of Biofuels and Biochemicals

The study on the effect of hydrodynamic flow on the photocatalytic performance of photocatalytic reactors