Comparative study of performance efficiency for three kinds of photoreactors

This paper generalized the structure characteristics of three different configuration photoreactors: annular type irradiated by lamp, solar shallow pond and solar flat plate and compared their performance efficiency at the same reaction condition level which was determined by the first order rate constant in photocatalytic decolorization of methyl orange in TiO 2 suspension. It was demonstrated that solar could be considered as an alternative light source in photoreactors not only for low running and construction cost but also for their successful performance. The evidence has proved the feasibility of solar photocatalytic oxidation as an additional or alternative advantage stage of wastewater treatment process.

Constructing S-scheme 2D/0D g-C_(3)N_(4)/TiO_(2) NPs/MPs heterojunction with 2D-Ti3AlC2 MAX cocatalyst for photocatalytic CO_(2) reduction to CO/CH_(4) in fixed-bed and monolith photoreactors

Exfoliated 2D MAX Ti_(3) AlC_(2) conductive cocatalyst anchored with g-C_(3)N_(4)/TiO_(2) to construct 2D/0D/2D het-erojunction has been explored for enhanced CO_(2) photoreduction in a fixed-bed and monolith photoreac-tor.The TiO_(2) particle sizes(NPs and MPs)were systematically investigated to determine effective metal-support interaction with faster charge carrier separation among the composite materials.When TiO_(2) NPs were anchored with 2D Ti_(3) AlC_(2) MAX structure,10.44 folds higher CH_(4) production was observed com-pared to anchoring TiO_(2) MPs.Maximum CH_(4) yield rate of 2103.5μmol g^(−1) h^(−1) achieved at selectivity 96.59%using ternary g-C_(3)N_(4)/TiO_(2)/Ti_(3) AlC_(2)2D/0D/2D composite which is 2.73 and 7.45 folds higher than using binary g-C_(3)N_(4)/Ti_(3) AlC_(2) MAX and TiO_(2) NPs/Ti_(3)AlC_(2) samples,respectively.A step-scheme(S-scheme)photocatalytic mechanism operates in this composite,suppressed the recombination of useful electron and holes and provides higher reduction potential for efficient CO_(2) conversion to CO and CH_(4).More im-portantly,when light intensity was increased by 5 folds,CH_(4) production rate was increased by 3.59 folds under visible light.The performance of composite catalyst was further investigated in a fixed-bed and monolith photoreactor and found monolithic support increased CO production by 2.64 folds,whereas,53.99 times lower CH_(4) production was noticed.The lower photocatalytic activity in a monolith photore-actor was due to lower visible light penetration into the microchannels.Thus,2D MAX Ti_(3) AlC_(2) composite catalyst can be constructed for selective photocatalytic CO_(2) methanation under visible light in a fixed-bed photoreactor.

Solar photocatalytic pathogenic disinfection:Fundamentals to state-of-the-art

It is necessary to treat pathogen-infected water before its utilisation.Of conventionally used treatment methods,solar photocatalysis has gained considerable momentum owing to its operational simplicity and capacity to use freely and abundantly available solar energy.This article systematically reviewed the disinfection of water with photocatalysis.It addressed the concerns of microbial infection of water and the fundamentals behind its treatment with photocatalysis.It presented an in-depth description of pathogenic deactivation with powerful reactive oxygen species.Special emphasis was given to process intensification as it is an attractive technique that provides multifunctionality and/or equipment miniaturisation.Solar reactor design regarding mobilised/immobilised photocatalysts and compound parabolic concentrators were elucidated.Finally,key parameters governing photoperformance,corresponding trade-offs,and the need for their optimisation were discussed.Overall,this article is a single point of reference for researchers,environmentalists,and industrialists who address the ever-severing challenge of providing clean water whilst also maintaining energy sustainability.

A Novel Multi-Tube Photoreactor with UV Light and Immobilized TiO_2 Thin Film for Water Treatment

A novel multi-tube photoreactor with 0.0188m3 valid reaction volume was constructed in pilot-scale. This rectangular reactor consisted of 13 regularly distributed silica glass tubes coating with TiO2 thin film photo-catalyst. Total active area of TiO2 thin film is 0.3916m2. The ratio of surface area to volume achieves 20.8m-1. Photocatalytic experiment of phenol red demonstrates that the apparent reaction rate constant (k) is 0.074 65 h-1 and 0.16502h-1 for reaction system with and without micro-bubbles mixing. The corresponding apparent quantum efficiency (a) is 8.1771 X 10-7g.J-1 and 4.9036 x 10-7g-J-1, respectively. COD value of reactant could decrease to 17mg.L-1 and high performance liquid chromatography (HPLC) only shows two absorption peaks in 24 h pho-tocatalytic process time, so this photoreactor has good photomineralization effect. Experimental results reveal that photocatalytic destruction of organics is possible by using the multi-tube photoreactor.

Evaluation of the plasmonic effect of Au and Ag on Ti-based photocatalysts in the reduction of CO2 to CH4

Crystalline TiO（P25） and isolated titanate species in a ZSM-5 structure（TS-1） were modified with Au and Ag, respectively, and tested in the gas-phase photocatalytic COreduction under high purity conditions. The noble metal modification was performed by photodeposition. Light absorbance properties of the catalysts are examined with UV–Vis spectroscopy before and after the activity test. In the gas-phase photocatalytic COreduction, it was observed that the catalysts with Ag nanostructures are more active than those with Au nanostructures. It is thus found that the energetic difference between the band gap energy of the semiconductor and the position of the plasmon is influencing the photocatalytic activity.Potentially, plasmon excitation due to visible light absorption results in plasmon resonance energy, which affects the excitation of the semiconductor positively. Therefore, an overlap between band gap energy of the semiconductor and metal plasmon is needed.

Nanohybrid membrane in algal-membrane photoreactor: Microalgae cultivation and wastewater polishing

Microalgae cultivation has gained tremendous attention in recent years due to its great potential in green biofuel production and wastewater treatment application. Membrane technology is a great solution in separating the microalgae biomass while producing high quality of permeate for recycling. The main objective of this study was to investigate the filtration performance of Ag/GO-PVDF(silver/graphene oxide-polyvinylidene fluoride) membrane in an algalmembrane photoreactor(A-MPR) by benchmarking with a commercial PVDF(com-PVDF) membrane. In this study, Chlorella vulgaris microalgae was cultivated in synthetic wastewater in an A-MPR for ammoniacal-nitrogen and phosphorus recovery and the wastewater was further filtered using Ag/GO-PVDF and com-PVDF membranes to obtain high quality water. Spectrophotometer was used to analyze the chemical oxidation demand(COD), ammoniacal nitrogen(NH3-N) and phosphate(PO43-). The concentration of proteins and carbohydrates was measured using Bradford method and phenol-sulfuric acid method, respectively. The COD of the synthetic wastewater was reduced from(180.5 ± 5.6) ppm to(82 ± 2.6) ppm due to nutrient uptake by microalgae. Then, the Ag/GO-PVDF membrane was used to further purify the microalgae cultivated wastewater, resulting in a low COD permeate of(31 ± 4.6) ppm. The high removal rate of proteins(100%) and carbohydrates(86.6%) as the major foulant in microalgae filtration, with low membrane fouling propensity of Ag/GO-PVDF membrane is advantageous for the sustainable development of the microalgae production. Hence, the integrated A-MPR system is highly recommended as a promising approach for microalgae cultivation and wastewater polishing treatment.

Interface and Quality of Nanometer TiO_2 Coated Optical Fiber

The interface and quality of TiO_2 coated optical fiber,which is obtained by dipping nude fibers into TiO_2 slurry,were investigated. The coating processes were carried out under different designed conditions,including various adhesives,solid content of TiO_2 slurry,times of cladding and followed heat-treat temperature. The interface and coating qualities were observed by scanning electron microscope. Coating defects,such as cracking,breaking off and the inhomogeneity of the cladding corresponds to different coating condition were analyzed. As a result, a well-combined and durable TiO_2 coating in optical fiber surface was obtained under definite optimizing experimental conditions and parameters.

Solar Oxidation and Removal of Arsenic from Groundwater Utilizing a Semicircular Section Tubular Photoreactor

A semicircular section tubular photoreactor has been constructed, characterized and applied to the treatment of groundwater contaminated with As（V） by means of the SORAS （solar oxidation and removal of arsenic） technique, using ferrous and citrate salts. The solar concentrator was built with recyclable waste materials： glass tubes from fluorescent lamps and 6-inch diameter PVC pipes cut in half and covered by aluminum foil. The reactor concentrates solar radiation up to 2.8 times its natural intensity. Batch irradiation experiments followed by controlled agitation （shear rate = 30-33 s^-1; 20 min agitation period） showed that the photoreactor accelerates the formation of settleable floccules （Dp 〉 0.5mm）, compared with a fluorescent lamp glass tube alone and a 2 L PET （polyethylene terephthalate） bottle. Irradiation times necessary for floccule formation in the photoreactor, the fluorescent lamp tube and the PET bottle were 15 min, 25 min and 60 min, respectively. Continuous flow experiments using a photoreactor with a photo-collection area of 0.9 m^2 and a hydraulic retention time （equal to the irradiation time） of 15 rain showed that immediate formation of floccules of good settleability occurs when the solution is subjected to moderate agitation （33 s^-1）. An efficiency of 98.36% for As（V） removal was obtained with a final concentration of 16.5 ktg/L in decanted waters. In accordance to these results, the photoreactor is able to treat approximately 130 L/m^2 within a 5-h period with UVA irradiation intensities of 50-70 W/mE.

Progress on gas-solid phase photoreactor and its application in CO_(2) reduction

The burgeoning field of photocatalytic reduction of CO_(2)has emerged as a remarkable promising solution to address some of the most pressing global energy and environmental issues which we face today.Researchers around the global have been striving to augment the efficiency of CO_(2)photocatalytic reduction,employing strategies that range from modifying the fundamental properties of photocatalysts to suppress the electron-hole recombination,optimizing reaction conditions to achieve the highest yield,and conceptualizing and constructing photoreactors to improve the adsorption process.Among these factors,the photoreactor plays a critical role in enhancing the overall photocatalytic efficiency.Understanding the various types of photoreactors and their operational dynamic can significantly influence the experimental design,thus guiding the data collecting and analysis.Compared to the solid-liquid phase,gas-solid phase photocatalytic reduction of CO_(2)is gaining recognition for its potential advantages,such as rapid molecular diffusion rates,adjustable CO_(2)concentrations,and uniform and sufficient light exposure.Nonetheless,the currently reported gas-solid phase photoreactors are still in their infancy.In this review,we dissect the underlying mechanism of photocatalytic CO_(2)reduction and the performance evaluation criteria of photoreactors,and review the development process of gas-solid phase photoreactors.Furthermore,we explore the evolution of gas-solid phase photoreactors,elucidating their growth trajectory and future possibilities.We present a comprehensive classification of gas-solid phase photoreactors,offering a new insight into their design and functionality,summarizing their strengths and inevitable limitations.Finally,we provide a forward-looking perspective on the future developmental prospects of carbon neutrality.

Photocatalytic degradation of 4-tert-octylphenol in a spiral photoreactor system

A spiral photoreactor system （SPS） was developed for the degradation of 4-tert-octylphenol （4-t-OP） in aqueous phase. 4-t-OP was previously considered as a endocrine disrupting compound frequently present in water. The direct photodegradation reaction caused by the SPS was found to accord with the characteristic of apparent first-order reaction with reaction rate constant k = 4.8 x 10-2 min-1. However, the direct photodegradation reaction could not make the 4-t-OP mineralized. The photodegradation efficiency increased from 88% to 91.2% in 45 min irradiation period after the internal surface of SPS was sintered with TiO2 thin film as catalyst. Catalyst concentration, number of catalyst coating layers and initial concentration of 4-t-OP were proven to be the factors affecting the photocatalytic degradation performance of the SPS on aqueous 4-t-OP. The degradation mechanism was investigated and the byproducts were analyzed using total organic carbon analyzer （TOC） and LC-MS. The possible chemical structures of the products were suggested. SPS with single layer of TiO2 prepared by sintering 13.6% of TiO2 precursor was proven to be more efficient than most of previous systems for removal of 4-t-OP from aqueous phase. 28.3% of the 4-t-OP was mineralized in 45 min according to the decreased amount of TOC value.

Mercury removal performance over a Ce-doped V-W/TiO_(2) catalyst in an internally illuminated honeycomb photoreactor

A new type of internally illuminated honeycomb photoreactor was designed. The honeycomb catalyst prepared by using Cedoped TiO2 with 1%–2% vanadium and tungsten was employed for mercury removal from simulated industrial flue gas. The adsorption kinetics in the reaction process were studied. The results showed that the internally illuminated honeycomb photoreactor had good mercury removal performance. When the temperature was 25℃ and the ultraviolet(UV) light intensity reached 80 μW/cm2, the mercury removal efficiency reached 92.5%. The mercury removal efficiency increased significantly with the doping ratio of Ce. XPS analysis showed that the oxidation state of Ce changed from 4 to 3 in the mercury removal reaction and produced lattice oxygen, which acts as an oxidant. O2 can promote mercury removal by honeycomb catalysts;SO2 and HCl also had positive effects, while NO had an inhibitory effect on mercury removal. Kinetic research in the reaction process showed that the quasi-first-order dynamic model had good fitting results, and the correlation coefficients of the fitting results for multiple sets of experimental data were more than 0.999.

Ag–AgBr/TiO_2/RGO nanocomposite:Synthesis,characterization,photocatalytic activity and aggregation evaluation

Ag-AgBr/TiO2 supported on reduced graphene oxide （Ag-AgBr/TiO2/RGO） with different mass ratios of grapheme oxide （GO） to TiO2 were synthesized via a facile solvothermal-photo reduction method. Compared to the single-, two- and three-component nanocomposites, the four-component nanocomposite, Ag-AgBr/TiO2/RGO-1 with mass ratio of GO to TiO2 at 1%, exhibited a much higher photocatalytic activity for the degradation of penicillin G （PG） under white light-emitting diode （LED-W） irradiation. The PG degradation efficiency increased with the increase of mass ratio of GO to TiO2 from 0.2% to 1%, then it decreased with the increase of mass ratio of GO to TiO2 from 1% to 5%. The zeta potentials of RGO-nanocornposites became more negative with the presence of humic acid （HA） due to the negatively charged HA adsorption, resulting in the shift of points of zero charge to lower values of pH. The aggregations of nanocomposites were more significant due to the bridging effect of HA. Furthermore, the aggregated particle sizes were larger for ROO-nanocomposites compared to other nanoparticles, due to the bindings of the carboxylic and phenolic functional groups in HA with the oxygen-containing functional groups in the RGO-nanocomposites. The microfiltration （MF） membrane was effective for the nanocomposites separation. In the continuous flow through submerged membrane photoreactor （sMPR） system, backwashing operation could efficiently reduce membrane fouling and recover TiO2, and thus indirectly facilitate the PG removal.

Theoretical study on flow and radiation in tubular solar photocatalytic reactor

In this paper,based on the mixture flow model,an optimized six-flux model is first established and applied to the tubular solar photocatalytic reactor.Parameters influencing photocatalyst distribution and radiation distribution at the reactor outlet,viz.catalyst concentration and circulation speed,are also analyzed.It is found that,at the outlet of the reactor,the optimized six-flux model has better performances(the energy increase by 1900%and 284%,respectively)with a higher catalyst concentration(triple)and a lower speed(one third).