The combination of rotating disk photocatalytic reactor and TiO2 nanotube arrays for environmental pollutants removal

The spinning disc reactor for photocatalytic degradation: A systematic review

In recent years, the use of a horizontal spinning disc reactor (SDR) as a photocatalytic reactor for the degradation of various pollutants in aqueous solutions has increased. This study was searched based on the PRISMA method. Two autonomous researchers carried out for the relevant studies using Scopus, Web of Science (WOS), and Science Direct databases. The search terms expanded focusing on the performance of horizontal spinning disc photocatalytic reactor (SDPR). In this review article, the main objective of the effect of operational factors on the efficiency of the degradation of pollutants with changes in the type of light source (range of visible light and UV radiation), disc rotational speed, flow rate, initial concentration of pollutants, pH, type of disc structure and flow regime are considered. Current challenges in SDPR include issues such as limited mass transfer, uneven light distribution, and difficulties in scaling up. To overcome these challenges, improvements can be made by optimizing reactor design for better mass transfer, enhancing light distribution through advanced light sources or reactor configurations, and developing scalable models that maintain efficiency at larger scales. Additionally, the use of innovative materials and coatings could improve the overall performance of SDPR.

Boosting environmental remediation: harnessing the efficiency of graphitic carbon nitride stabilized on red ocher surface for enhanced photocatalytic remove of Escherichia coli

In the present study, the antibacterial effect of graphitic carbon nitride coated on the red ocher was investigated by the photocatalytic process to remove Gram-negative Escherichia coli bacteria. The concentration effects (0.025, 0.05, and 0.1 g/mL) of disinfectant, contact time (30, 60, and 90 min), and the number of bacteria (102, 104, and 106 CFU/mL) were examined. In this research, in each experiment, 100 mL of the sample was taken, and the test work was performed. The red ocher required for this project was obtained from Hormoz Island, Hormozgan Province, Iran. Melamine was used for the synthesis and manufacture of graphitic carbon nitride. A general-purpose media was used for microbial culture using the pour and spread plate methods, as well as an LED lamp with a wavelength of 420 nm as a light source for the photocatalytic process. To obtain the important factors, the interaction of the factors and the optimal experimental design were used through the response surface methodology (RSM) based on the Box-Behnken design. According to research findings, this method is effective in eliminating E. coli. The results showed that the increase in the amount of disinfectant from 0.025 to 0.1 g/mL and also the increase of contact time from 30 to 90 min accelerated the removal rate of E. coli. The numerical value of R2 obtained for the removal of E. coli was 0.9728, indicating good agreement between experimental and predicted data. Therefore, its utilization in water disinfection seems necessary, both to ensure human health and environmental protection.

Synthesis of TiO2 nanotubes from ilmenite with CuS nanoparticles as efficient visible-light photocatalyst

Titanium dioxide nanotube (TNT) is one of the most widely used photocatalysts. In this research, TNT was prepared by a facile method using ilmenite (FeTiO3) concentrate as the titanium source. For this purpose, iron was leached out from ilmenite using HCl in assistance with the iron powder as the reducing agent to produce pure TiO2, where consequently, TNT was produced through hydrothermal treatment of the prepared TiO2 in an alkaline solution. CuS quantum dots, using the L-cysteine as a linker, were coated on the TNT to improve TNTs' photocatalytic properties. Characterization was done using XRD, SEM, FESEM, HRTEM, FT-IR, nitrogen sorption, and band gap measurement. The results revealed the formation of TNT with a star-shaped macrostructure as well as, a good dispersion of uniform CuS quantum dots with an average diameter of a few nanometers on the TiO2 structure. A dye adsorption kinetics study of the TNT and CuS-dopped TNT showed that TNT carries a higher adsorption capacity compared to the CuS-dopped TNT, developed due to its higher surface area and pore volume. Next, the photocatalytic performance (under visible light) of the prepared composite was studied over the methylene blue (MB) and malachite green (MG) dyes, after the determination of the dye adsorption equilibrium point (where the adsorption stops). TNT showed almost no dye degradation while the prepared composite degraded almost 95 % of the dyes as the result of the reduced band gap from 3.21 to 2.67 eV. In this study, for the first time, the TNT was prepared using a mineral source and ilmenite, enhanced in photocatalytic properties, and presented a successful application.

Recent Developments of Light-Harvesting Excitation, Macroscope Transfer and Multi-Stage Utilization of Photogenerated Electrons in Rotating Disk Photocatalytic Reactor

The rotating disk photocatalytic reactor is a kind of photocatalytic wastewater treatment technique with a high application potential, but the light energy utilization rate and photo quantum efficiency still need to be improved. Taking photogenerated electrons as the starting point, the following contents are reviewed in this work: (1) Light-harvesting excitation of photogenerated electrons. Based on the rotating disk thin solution film photocatalytic reactor, the photoanodes with light capture structures are reviewed from the macro perspective, and the research progress of light capture structure catalysts based on BiOCl is also reviewed from the micro perspective. (2) Macroscope transfer of photogenerated electrons. The research progress of photo fuel cell based on rotating disk reactors is reviewed. The system can effectively convert the chemical energy in organic pollutants into electrical energy through the macroscopic transfer of photogenerated electrons. (3) Multi-level utilization of photogenerated electrons. The photogenerated electrons transferred to the cathode can also generate H2O2 with oxygen or H2 with H+, and the reduction products can also be further utilized to deeply mineralize organic pollutants or reduce the nitrate in water. This short review will provide theoretical guidance for the further application of photocatalytic techniques in wastewater treatment.

Textile Wastewater Treatment in a Spinning Disc Reactor: Improved Performances—Experimental, Modeling and SVM Optimization

The paper presents an experimental study regarding the treatment of a real textile wastewater using the spinning disc (SD) technology, either individually or associated with an advanced Fenton oxidation step. The SD efficiency was investigated by studying the color, suspended solids, or turbidity removals, at distinctive feeding flowrates (10–30 L/h) and disc rotating speeds (100–1500 rpm). The data revealed increasing removal trends and allowed to establish the highest removal values. Based on obtained experimental results, the wastewater treatment efficiency by SD technology was reasonably good and thus, the WW indicators can be improved within relatively short periods of time. Additionally, based on supervised learning algorithms, the study includes treatment modeling for turbidity and color removal, followed by turbidity removal optimization relying on the best learned models. Satisfactory results obtained with the modeling and optimization procedures provide useful predictions for the approached treatment processes. Furthermore, within this study, a Fenton oxidation process was applied to SD technology to minimize the color and solids content. The influence of pH, hydrogen peroxide and ferrous ions concentrations was also investigated in order to establish the highest removal efficiencies. Overall, the SD technology applied in textile effluents treatment proved to be an appropriate and efficient alternative to classical mechanical step applied within the primary treatment step and, when associated with an advanced oxidative process in the secondary step, rendered good improvement, namely of 62.84% and 69.46% for color and respectively, suspended solids removal.

A review: Application of tourmaline in environmental fields

Heavy metals and organic pollutants could pose long-term threats to the ecosystem and human health, so it is urgent for us to find a friendly and efficient material to remove pollutants in environment. Since tourmaline is widely distributed in natural environment and has many excellent physical and chemical properties including radiating far infrared energy, permanently releasing negative ions, producing an electrostatic field, releasing rare microelements, and stimulating the growth and metabolism of microorganisms and plants, tourmaline had been conducted to alleviate environmental pollution. This review summarizes the application of tourmaline in aqueous solutions and soil polluted by heavy metals and organic pollutants, the factors that affect the removal of pollutants by tourmaline and the removal mechanisms. In addition, to ensure the safe use of tourmaline, this review also elaborates the environment risks of tourmaline through its toxicity indexes to soil and plant.

Textile Wastewater Treatment on a Spinning Disc Reactor: Characteristics, Performances, and Empirical Modeling

Spinning disc (SD) technology has been successfully applied, for the first time, in real textile wastewater treatment with no other additional processing. The SD efficiency was investigated using real textile effluents to study the color and suspended solids removals at different effluent-supplying flowrates (10–30 L/h) and different disc rotational speeds (100–1500 rpm) with good experimental results; thus, it can minimize the polluting loads within a short time period. Furthermore, within this study, process modeling and its classical optimization were applied to SD technology for wastewater treatment. The experiments were organized according to an active central composite rotatable 23 order design, considering as independent variables the wastewater flowrate, rotational speed, and operating time and, as optimization criteria, the suspended solids removal and discoloration degree. Overall, this novel study proved that the SD technology applied in textile effluent treatment is a suitable alternative to a primary mechanical step.

A Semi-Pilot Photocatalytic Rotating Reactor (RFR) with Supported TiO₂/Ag Catalysts for Water Treatment

A four stage semi-pilot scale RFR reactor with ceramic disks as support for TiO₂ modified with silver particles was developed for the removal of organic pollutants. The design presented in this article is an adaptation of the rotating biological reactors (RBR) and its coupling with the modified catalyst provides additional advantages to designs where a catalyst in suspension is used. The optimal parameter of rotation was 54 rpm and the submerged surface of the disks offer a total contact area of 387 M². The modified solid showed a decrease in the value of its bandgap compared to commercial titanium. The system has a semi-automatic operation with a maximum reaction time of 50 h. Photo-activity tests show high conversion rates at low concentrations. The results conform to the Langmuir heterogeneous catalysis model.

Evaluation of performance with small and scale-up rotating and flat reactors; photocatalytic degradation of bisphenol A, 17β-estradiol, and 17α-ethynyl estradiol under solar irradiation

In this study, the performances of photocatalytic reactors of the small and scale-up rotating and flat types were evaluated to investigate the treatment of new emerging contaminants such as bisphenol A (BPA), 17α-ethynyl estradiol (EE2), and 17β-estradiol (E2) that are known as endocrine disrupting compounds (EDCs). In the laboratory tests with the small-scale rotating and flat reactors, the degradation efficiencies of the mixed EDCs were significantly influenced by the change of the hydraulic retention time (HRT). In particular, considering the effective two-dimensional reaction area with light and nanotubular TiO₂ (NTT) on a Ti substrate, the rotating reactors showed the more effective performance than the flat reactor because the degradation efficiencies are similar in the small effective area. In addition, the major parameters affecting the photocatalytic activities of the NTT were evaluated for the rotating reactors according to the effects of single and mixed EDCs, the initial concentrations of the EDCs, the UV intensity, and dissolved oxygen. In the extended outdoor tests with the scale-up photocatalytic reactors and NTT, it was confirmed from the four representative demonstrations that an excellent rotating-reactor performance is consistently shown in terms of the degradation of the target pollutants under solar irradiation.

A bio-inspired inner-motile photocatalyst film: a magnetically actuated artificial cilia photocatalyst

A new type of inner-motile photocatalyst film is explored to enhance photocatalytic performance using magnetically actuated artificial cilia. The inner-motile photocatalyst film is capable of generating flow and mixing on the microscale because it produces a motion similar to that of natural cilia when it is subjected to a rotational magnetic field. Compared with traditional photocatalyst films, the inner-motile photocatalyst film exhibits the unique ability of microfluidic manipulation. It uses an impactful and self-contained design to accelerate interior mass transfer and desorption of degradation species. Moreover, the special cilia-like structures increase the surface area and light absorption. Consequently, the photocatalytic activity of the inner-motile photocatalyst film is dramatically improved to approximately 3.0 times that of the traditional planar film. The inner-motile photocatalyst film also exhibits high photocatalytic durability and can be reused several times with ease. Furthermore, this feasible yet versatile platform can be extended to other photocatalyst systems, such as TiO2, P25, ZnO, and Co3O4 systems, to improve their photocatalytic performance.

Effect of matrix on the electrochemical characteristics of TiO₂ nanotube array-based PbO₂ electrode for pollutant degradation

A series of lead dioxide electrodes developed on titania nanotube arrays with different matrix were fabricated by electrodeposition. Before the deposition of PbO₂, the matrix of this anode was electrochemically reduced in (NH₄)₂SO₄ solution and/or pre-deposited with certain amounts of copper. To gain insight into these pretreatments, the PbO₂ electrodes were characterized by SEM, LSV, and XRD, and their electrocatalytic activities for pollutant degradation were compared using p-nitrophenol (p-NP) as a model. It was confirmed that the electrochemical reduction with (NH4)₂SO₄ resulted in the partial conversion of TiO₂ into Ti₄O₇ and Ti₅O₉, which increased the conductivity of PbO₂ anode, but decreased its electrochemical activity, while the Ti/TNTs*-Cu/PbO₂ electrode with both pretreatments possessed the highest oxygen evolution overpotential of 2.5 V (vs. SCE) and low substrate resistance. After a 180-min treatment on this electrode, the removal efficiency of p-NP reached 82.5% and the COD removal achieved 42.5% with the energy consumption of 9.45 kWh m(-3), demonstrating the best performance among these electrodes with different matrices. Therefore, this titania nanotube array-based PbO₂ electrode has a promising application in the industrial wastewater treatment.

Degradation of 2,4-Dichlorophenoxyacetic Acid (2,4-D) by Novel Photocatalytic Material of Tourmaline-Coated TiO₂ Nanoparticles: Kinetic Study and Model

The novel complex photocatalytic material was prepared by coating TiO₂ nanoparticles on tourmaline using the sol-gel method, and used in the degradation of the herbicide 2,4-D. The results indicated that coating TiO₂ with tourmaline enhanced the photocatalytic activity significantly. Based on the research of a simplified model for the average light intensity in the photoreactor, the influence of the concentration of photocatalyst, and the initial concentration of 2,4-D, a model for the degradation of 2,4-D by the tourmaline-coated TiO₂ nanoparticles was established. Further tests showed that results calculated from this model were close to those obtained in the actual experiments.

Functionalized nanoparticle interactions with polymeric membranes

A series of experiments was performed to measure the retention of a class of functionalized nanoparticles (NPs) on porous (microfiltration and ultrafiltration) membranes. The findings impact engineered water and wastewater treatment using membrane technology, characterization and analytical schemes for NP detection, and the use of NPs in waste treatment scenarios. The NPs studied were composed of silver, titanium dioxide, and gold; had organic coatings to yield either positive or negative surface charge; and were between 2 and 10nm in diameter. NP solutions were applied to polymeric membranes composed of different materials and pore sizes (ranging from ≈ 2 nm [3 kDa molecular weight cutoff] to 0.2 μm). Greater than 99% rejection was observed of positively charged NPs by negatively charged membranes even though pore diameters were up to 20 times the NP diameter; thus, sorption caused rejection. Negatively charged NPs were less well rejected, but behavior was dependent not only on surface functionality but on NP core material (Ag, TiO(2), or Au). NP rejection depended more upon NP properties than membrane properties; all of the negatively charged polymeric membranes behaved similarly. The NP-membrane interaction behavior fell into four categories, which are defined and described here.

Degradation of rhodamine B using an unconventional graded photoelectrode with wedge structure

A graded TiO(2)/Ti round disk photoelectrode with a wedge structure is proposed, fabricated, and used in a rotating disk photoelectrocatalytic (PEC) reactor for the first time. In addition to improved light utilization efficiency resulting from multiple reflections of radiation light on the wedge surface, enlarged surface area enables the electrode to carry more pollutants for treatment. Compared with the conventional planar electrode with same diameter, the wedge-surface electrode showed much lower light reflectivity (<0.014 versus 0.306), larger photocurrent and better treatment performance. For model dye wastewater containing Rhodamine B (RB) at concentrations ranging from 20 to 150 mg · L(-1), wedge-surface electrode removed 100-79% total color in 60 min and 93-28% COD in 150 min, much higher than 69-28% and 50-4% obtained using the planar electrode under the same experimental conditions. Experimental results demonstrated that the wedge-surface electrode works efficiently and has great potential for treating high concentration dye wastewater.