Photocatalytic wastewater treatment technology has been proposed for more than 30 years, but it is still seldom used in industry. The lack of research on high-performance and cost-effective photocatalytic wastewater treatment reactors (PWTRs) may be one of the major reasons limiting the industrial application of photocatalytic technology. To accelerate the realization of industrial application, this review emphasizes the importance of increased research on PWTRs. In this review, we analyze the role of photocatalytic technology in wastewater treatment, followed by a comprehensive discussion of PWTR design from multiple perspectives, including photocatalyst selection, loading and recovery method of photocatalysts within the reactor, light source design, and reaction conditions control. Additionally, we consider the cost of reactor design. Finally, we summarize the optimization strategy of PWTRs and the criteria for evaluating photocatalytic performance. The main innovation of this review lies in a comprehensive analysis of PWTR design, with a focus on cost-effective and high-performance solutions to promote the industrial use of photocatalytic technology.

A three-layered phosphor structure was designed and prepared by the spin coating of BaSi₂N₂O₂:Eu (cyan-emitting) and (Sr,Ca)AlSiN₃:Eu (red-emitting) phosphor films on the yellow-emitting Y₃Al₅O₁₂:Ce (YAG:Ce) phosphor ceramic synthesized by the solid-state reaction under vacuum sintering. In order to achieve high color rendering lighting, the influence of the composition and structure of the three-layered phosphors on the optical, thermal, and electrical properties of the chip-on-board (COB) packaged white-light-emitting diodes (WLEDs) was studied systematically. The WLED with the structure of “red+cyan+yellow” (R+C+Y) three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W, the fidelity index (R_f) of 93, the gamut index (R_g) of 97, and the correlated color temperature (CCT) of 3852 K. Under the excitation of laser diode (LD), the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W, color rendering index (CRI) of 90, and CCT of 5988 K. The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.

Light-emitting diodes (LEDs) have been regarded as the best artificial source of light for a plant factory. However, the effect of light quality on seedling production in such environments requires further study. On the basis of the practical application of light on cucumber seedlings (Ansha Company) in plant factories, the present investigation tracked and recorded the specific effects of red and blue light on the growth of the seedlings by analyzing the photo-biological mechanism involved. The growth parameters, as well as the photosynthetic characteristics of cucumber seedlings, were measured at different variations of light quality. The results showed that when the proportion of red light in the light source was higher than blue light, the height of the seedlings, leaf size, stem diameter, Dixon Quality Index (DQI), relative chlorophyll content, and the net photosynthetic rate were higher than those of the experimental group with a relatively high proportion of blue light. In the case of R7B3 (70% red light and 30% blue light), the stem diameter, DQI, and net photosynthetic rate of seedlings were 14%, 57%, and 22% higher than the minimum value, respectively. The present study analyzed the influence of red and blue light on plant growth characteristics during actual production and provides standardization for it.

Owing to its stability and environment-friendly properties, the SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) phosphor has attracted major scientific interest.

Light-emitting diodes (LEDs) were the best artificial light source for plant factories. Red light-emitting diodes (LEDs, R) and blue light-emitting diodes (LEDs, B) were used to obtain different light intensities of uniform spectra, and the greenhouse environment was considered as a comparison. The results showed that root dry weight, shoot dry weight and stem diameter were superior in plant growth under 240 μmolm^-2s^-1, additionally, the Dixon Quality Index (DQI) was also best. Under 240 μmolm^-2s^-1, the net photosynthesis rate (Pn) was consistent with the greenhouse’s treatment, superior to other experimental groups. The results implied that the PPFD was more suitable for the cultivation of tomato seedlings under the condition of 240 μmolm^-2s^-1, and can replace the greenhouse conditions so as to save energy and reduce emissions.