Optimization of toluene removal over W-doped TiO2 nano-photocatalyst under visible light irradiation

Enhancing air treatment through controlled fabrication of transition metal-doped titanium dioxide nanocomposites for photocatalytic toluene degradation

Rapid industrial growth and urbanization have resulted in a significant rise in environmental pollution issues, particularly indoor air pollutants. As a result, it is crucial to design and develop technologies and/or catalysts that are not only cost-effective but also promising high performance and practical applicability. However, achieving this goal has been so far remained a challenging task. Herein, a series of transition metal M - TiO2 (M = W, Fe, Mn) nanocrystals was prepared for photocatalytic degradation of volatile organic compounds (VOCs), i.e., toluene. Of the nanocomposites tested, W-TiO2 showed significantly improved photocatalytic activity for VOC degradation under UV irradiation compared to the others. In particular, the optimized W dopant amount of 0.5 wt% resulted in the outstanding degradation performance of toluene (96%) for the obtained W-TiO2(0.5%) nanocomposite. Moreover, W-TiO2(0.5%) nanocomposite exhibited good stability for 32 h working under high toluene concentration (10 ppm) compared to the pristine TiO2. The current work demonstrates the potential usage of M - TiO2 nanocrystals, particularly W-TiO2(0.5%), as a promising photocatalyst for efficient VOCs degradation.

Water treatment by forward osmosis using novel D-Xylose coated magnetic nanoparticles as draw agent

In this study, D-Xylose coated MNPs were synthesized and used as draw agent in forward osmosis (FO) process for water purification. Response surface methodology (RSM) was utilized for the design and optimization of synthesis parameters. In order to characterize the synthesized MNPs, FTIR, TEM, VSM, and UV characterization techniques were performed. The effect of independent parameters including D-Xylose mass, MNPs mass, and synthesis time on the osmotic pressure was investigated. Based on the optimization results, the osmotic pressure of a 2 wt./v% draw solution using 2.66 g D-Xylose, 0.13 g MNPs, and a 7.11 h synthesis time was 0.81 bar as the highest value. Using D-Xylose coated MNPs as draw agent and deionized water as the feed, the initial FO water flux was 2.98 LMH. Reusing the recovered MNP draw agent in two more consecutive tests resulted in the reduction of water flux to 2.68 and 2.30 LMH, respectively. Moreover, using 0.01 M NaCl solution as the feed, the initial water flux was reported as 1.3 LMH. To remove the draw agents from suspension, external magnetic field was applied to obtain a water turbidity of 0.08 NTU.

Synthesis and characterization of CuxO/Bi2O3 oxides for removal of HCHO under visible light irradiation

Cu_xO/Bi₂O₃ oxides grown on nickel foam were synthesized via an electrodeposition method to degrade indoor HCHO under visible light irradiation and fully characterized by XRD, SEM, FT-IR, and UV-Vis technologies. The characterization results showed that the Cu_xO/Bi₂O₃ oxides were successfully loaded on nickel foam and the visible light response spectrum was expanded to 740 nm. Plackett-Burman design combined with central composite design has been used to optimize factors that affect HCHO removal performance. The results demonstrated that bismuth nitrate content, polyethylene glycol 600 content, sintering time, and lactic acid concentration were the four most important factors affecting the HCHO removal performance over Cu_xO/Bi₂O₃ sample. The optimum Cu_xO/Bi₂O₃ sample could degrade 88.796% of HCHO in 300 min at the conditions of 4.28 mol/L lactic acid, 4.86% polyethylene glycol 600, 194.03 min sintering time, and 45.83 g bismuth nitrate, and the HCHO removal rate remained 82.3% after five cycles. A plausible mechanism for the degradation of HCHO under visible light irradiation was proposed. This work provides a feasible solution for removing indoor formaldehyde in the field of photocatalysis.

Desalination of brackish water by gelatin-coated magnetite nanoparticles as a novel draw solute in forward osmosis process

This paper presents the optimization of synthesis of gelatin-coated magnetite nanoparticles (MNPs) and their application as a draw solute in forward osmosis (FO) process. Persicaria bistorta root extract is used as the gelatin crosslinker, and its efficiency is compared with glutaraldehyde as a common crosslinker. Also, the impact of the concentration of gelatin and the draw solution on the osmotic pressure of the produced draw solution has been investigated using response surface methodology. Using Persicaria bistorta root extract as the crosslinker in the optimized conditions, the highest osmotic pressure (1.01 bar) was achieved in a concentration of 7.7%w/v and 14246 mg/l for gelatin and draw solution, respectively. Using glutaraldehyde under the same conditions resulted in osmotic pressure of 1.06 bar which is very close to the pressure found for Persicaria bistorta root extract (1.01 bar), confirming the benefit of the latter as a gelatin crosslinker. Further, using a solution with gelatin-coated MNPs as the draw solution, deionized water as the feed solution, and an osmotic pressure difference of 1.5 in the FO process generated an initial water flux of 1.54 LMH. By repeating the process in nine more cycles, the initial water flux was reduced to 0.365 LMH. These experiments confirm the as-prepared gelatin-MNPs as a promising draw solution in the FO process.

Granular-carbon supported nano noble-metal (Au, Pd, Au-Pd): new dual-functional adsorbent/catalysts for effective removal of toluene at low-temperature and humid condition

Treatment of the volatile organic compounds (VOCs) especially aromatic compounds such as toluene at low temperature and in the highly humid condition is currently a great challenge. New dual functional adsorbent/catalysts have been developed in this study to minimize the mass-transfer limitation at low temperature. The ready-to-practically-use materials, which consisted nano-sized noble metal (Au, Pd, Au-Pd) supported on granular carbon (GC) have been prepared using a metal-sol method. The surface morphology, and structure of these granular materials were characterized to confirm the presence of nano-sized noble metal on the GC as well as the properties of the dual functional adsorbent/catalyst. The results of catalytic performance revealed that the presence of Pd played an important role in the formation of nano Au particles, which were the catalytic active-site for toluene oxidation. At 60% relative humidity and 150°C the dual functional adsorbent/catalyst, Au-Pd/GC, exhibited 97.2% toluene removal. Importantly, the kinetic analysis for the catalytic oxidation of nano-sized 0.5%Au-0.27%Pd/GC catalyst showed that the Langmuir-Hinshelwood mechanism provided a good fit towards the experimental data and allowed to determine the kinetic parameters of the reaction-rate law -rA=k⋅KA⋅CA1+KA⋅CA⋅KO2⋅CO21+KO2.CO2. The activation energy, adsorption enthalpy of toluene, and oxygen on the catalyst were reported.

Synergetic effect between adsorption and photodegradation on rGO/TiO2/ACF composites for dynamic toluene gaseous removal

The toluene poses a serious threat to the atmospheric environment and human health. Herein, the reduced graphene oxide (rGO)/TiO₂ immobilized on the activated carbon fiber (ACF) are fabricated by ultrasonic assisted sol-gel impregnation method to photodegrade dynamic toluene. Characterizations of rGO/TiO₂/ACF composites reveal that the majority of graphene oxide (GO) is reduced to rGO and rGO/TiO₂ is evenly loaded onto the ACF surface in the form of a smooth film. Furthermore, the photoelectrochemical experiments demonstrate both rGO and ACF can enhance significantly the separation efficiency of electron-hole pairs. The maximum removal efficiency of rGO/TiO₂/ACF-0.75% can be up to 85% under ultraviolet irradiation. The rGO/TiO₂/ACF exhibits more excellent adsorption and photodegradation activity for dynamic toluene than both rGO/TiO₂ and ACF due to the synergetic effect rather than a simple linear combination of the rGO/TiO₂ and ACF for toluene conversion. The possible photodegradation pathway is proposed according to intermediates measured by GC-MS, and adsorption coupling photocatalytic mechanisms are discussed.

Green synthesis and optimization of nano-magnetite using Persicaria bistorta root extract and its application for rosewater distillation wastewater treatment

The aim of this research is to synthesize magnetite nanoparticles, using Persicaria bistorta root extract as the reducing agent, and to test its adsorption properties in the treatment of rosewater distillation wastewater. Taking advantage of Taguchi method, effect of synthesis parameters, including molar concentration of FeCl₂, concentration of plant extract, temperature, and pH on crystallite size and magnetization strength is studied. Based on the successful synthesis of magnetite nanoparticles and characterization experiments, Persicaria bistorta root extract can be considered as a proper alternative as the reducing agent. Data analysis shows that crystallite size and magnetization are positively correlated with concentration of FeCl₂ and pH, while inversely related to temperature and independent of plant extract concentration. The optimum values achieved for concentration of FeCl₂, temperature, and pH are 0.15 M, 70 °C, and 11, respectively, with the production of nanoparticles with magnetite size of 45.5 nm and magnetization value of 62.5 emu/g. In addition, the application of as-synthesized magnetite nanoparticles as an adsorbent for treatment of rosewater distillation wastewater proved its high adsorption capacity for chemical oxygen demand (COD) up to 149 mg/g. Adsorption data also shows a good fitness with Langmuir and Freundlich isotherm models.

Synthesis, characterization and evaluations of TiO2 nanostructures prepared from different titania precursors for photocatalytic degradation of 4-chlorophenol in aqueous solution

BACKGROUND

The aim of present work, was to synthesize the titanium nanoparticles (TNPs) and titanium nanotubes (TNTs) through the hydrothermal method with different precursors including the Titanium(IV) isopropoxide (TTIP) and Titanium(IV) bis(ammonium lactato)dihydroxide (TALH).

METHODS

TiO₂ nanostructures from different titania precursors as heterogeneous photocatalysis via hydrothermal method were synthesized. The as-prepared photocatalysts were characterized by X-ray diffraction, UV-Vis diffuse reflectance spectra, surface area measurements, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The TiO₂ photocatalysts were tested on the degradation of 4-Chlorophenol (4-CP) aqueous solution under UVC irradiation in a fabricated photoreactor.

RESULTS

The effect of operating parameters including the; initial 4-CP concentration (50-150 mg/L), catalyst dosages (0-3 g/L) and solution pH (4-10) on the photocatalytic activity of the prepared catalysts were systematically investigated. The results show that amongst the TiO₂ nanostructures under best conditions (initial 4-CP concentration of 50 mg/L, catalyst dosage of 2 g/L, pH of 4.0, Time of 180 min) TNT-P2 exhibited much higher photocatalytic degradation efficiency (82%) as compared with TNT-P1 (77%), TNP-P2 (51%), and TNP-P1 (48%). Moreover, the mechanism and tentative pathways of 4-CP degradation were explored. Finally, the kinetic study was performed and the Langmuir-Hinshelwood kinetic model was aptly fitted with the experimental data.

CONCLUSION

The results of the photocatalytic activity measurement demonstrated that one-dimensional TNTs shows enhanced photocatalytic performance as compared to the TNPs, therefore, indicating the beneficial feature of TNTs as a photocatalyst for the degradation of pollutants. Besides, TiO₂ nanostructures prepared from TALH precursor (TNT-P2 82%, TNP-P2 51%) has higher photocatalytic degradation efficiency as compared with TTIP precursors (TNT-P1 77%, TNP-P1 48%).