Formal quantum efficiencies for the photocatalytic reduction of CO2 in a gas phase batch reactor

Rational design of α-MnO2/HT-GCN nanocomposite for effective photocatalytic degradation of ciprofloxacin and pernicious activity

The present study is mainly concerned with the development of cost-efficient composite material utilized to produce one-dimensional manganese oxide (α-MnO2) nanoparticles coated on two-dimensional graphitic carbon nitrides (HT-GCN) as nanocomposite (α-MnO2/HT-GCN) for highly efficient CIP degradation. The α-MnO2 nanoparticles (NPs) were prepared by a simple hydrothermal technique before being decorated on HT-GCN (H denotes protonation and T represents thermal-decomposition-graphitic carbon nitride). Tauc plots were used to calculate the band gap values of the photocatalysts α-MnO2 (1.74 eV), GCN (2.84 eV), HT-GCN (2.63 eV), and α-MnO2/HT-GCN (2.31 eV). The mechanism was investigated by various scavengers, particularly isopropanol (•OH) makes a significant role in the photodegradation process. The degradation percentage for ciprofloxacin was 89.2% and the rate of reaction R2 = 0.9913. This study demonstrates a unique method for developing a heterojunction-based nanocomposite of α-MnO2/HT-GCN, which exhibit better light absorption performance.

Designing reliable and accurate isotope-tracer experiments for CO2 photoreduction

The photoreduction of carbon dioxide (CO₂) into renewable synthetic fuels is an attractive approach for generating alternative energy feedstocks that may compete with and eventually displace fossil fuels. However, it is challenging to accurately trace the products of CO₂ photoreduction on account of the poor conversion efficiency of these reactions and the imperceptible introduced carbon contamination. Isotope-tracing experiments have been used to solve this problem, but they frequently yield false-positive results because of improper experimental execution and, in some cases, insufficient rigor. Thus, it is imperative that accurate and effective strategies for evaluating various potential products of CO₂ photoreduction are developed for the field. Herein, we experimentally demonstrate that the contemporary approach toward isotope-tracing experiments in CO₂ photoreduction is not necessarily rigorous. Several examples of where pitfalls and misunderstandings arise, consequently making isotope product traceability difficult, are demonstrated. Further, we develop and describe standard guidelines for isotope-tracing experiments in CO₂ photoreduction reactions and then verify the procedure using some reported photoreduction systems.

Recent advances in performance improvement of Metal-organic Frameworks to remove antibiotics: Mechanism and evaluation

Antibiotic pollution is a serious global problem, which may threaten the health of human and ecosystem. Thereinto, water pollution is the most common way. Thus, it is necessary to develop effective methods to remove antibiotics from the natural aqueous environments. Metal-organic Frameworks (MOFs) - based adsorption and photocatalysis strategies have been demonstrated to be efficient, environmental and promising methods to solve antibiotic pollution and repair the environment. In this review, several strategies to improve the properties of MOFs for removal were summarized and discussed. And the removal mechanisms were also discussed. Besides, new and more reliable evaluation methods of MOFs to remove antibiotics were presented, including preferential adsorption (q_p), quantum yields (QY), space time yields (SY) and figure of merit (FOM). This paper provides alternative perspectives for researchers to improve the properties of MOFs and raise analytic efficiency of antibiotic removal.

Preparation of TiO2-deposited silica-based catalysts for photocatalytic decomposition of chloro-pesticide to environmentally less toxic species

Herein, titanium (IV) oxide (TiO₂) loaded into montmorillonite (MK10) and sand is presented as an efficient heterogeneous catalyst for the degradation of 1,4-dichlorobenzene (DCB) as a model organic pollutant in the aqueous phase. The catalyst was synthesized by incorporating titanium isopropoxide as a precursor into MK10 through a simple solvent impregnation method, followed by direct calcination. The same protocol was applied to a clean quartz matrix. The resulting catalysts were characterized in detail using a variety of techniques. The TiO₂ deposited MK10 and sand exhibited photochemical removal of DCB (>99% of 100 mg L^-1) from the aqueous phase; this process followed a pseudo second-order kinetic model values in the range of Q_e:111-113 mg g^-1 and K₂: 4-5 × 10^-4 g mg^-1 min^-1. The kinetic plots indicate that after 30 min, the intermediates start to decrease and complete degradation occurs in 180 min. The modified materials showed fast DCB degradation kinetics under photochemical reaction conditions and adsorption under dark reaction conditions. The unmodified matrix adsorbed 99.12-99.88% of the DCB under both dark and light reaction conditions. These photocatalysts are stable, reusable, and least amount of titanium leaching. The simple two step synthesis, and high photocatalytic performance (with 10 mg of the catalyst without any oxidants) of our catalysts can be promising in environmental applications to treat similar organic pollutants in wastewater. These catalysts have enhanced activity and durability for environmental catalytic pollutant degradation reactions and can provide insights beyond single metal oxide catalysts for heterogeneous catalysis at diverse operating conditions.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

Improved Methane Production by Photocatalytic CO2 Conversion over Ag/In2O3/TiO2 Heterojunctions

In this work, the role of In₂O₃ in a heterojunction with TiO₂ is studied as a way of increasing the photocatalytic activity for gas-phase CO₂ reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In₂O₃, different behaviors appear. Thus, with the high crystallite sizes of commercial In₂O₃, the activity is improved with respect to TiO₂, with modest improvements in the selectivity to methane. On the other hand, when In₂O₃ obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH₄, even if the total conversion is lower than that obtained with TiO₂. The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In₂O₃, more pronounced when smaller particles are used as in the case of laboratory-made In₂O₃, as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium.

Heterojunction photocatalysts for degradation of the tetracycline antibiotic: a review

Antibiotic pollution is a major health issue inducing antibiotic resistance and the inefficiency of actual drugs, thus calling for improved methods to clean water and wastewater. Here we review the recent development of heterojunction photocatalysis and application in degrading tetracycline. We discuss mechanisms for separating photogenerated electron-hole pairs in different heterojunction systems such as traditional, p-n, direct Z-scheme, step-scheme, Schottky, and surface heterojunction. Degradation pathways of tetracycline during photocatalysis are presented. We compare the efficiency of tetracycline removal by various heterojunctions using quantum efficiency, space time yield, and figures of merit. Implications for the treatment of antibiotic-contaminated wastewater are discussed.

Photocatalytic activity of new nanostructures of an Ag(i) metal–organic framework (Ag-MOF) for the efficient degradation of MCPA and 2,4-D herbicides under sunlight irradiation

A new Ag(i) metal–organic framework (Ag-MOF) [Ag(p-OH-C₆H₄COOH)₂(NO₃)]_n [Ag(PHBA)₂(NO₃)]_n, (1) (PHBA: C₈H₆O₄ {p-hydroxybenzoic acid}) was synthesized using two different methods; the laying method (single crystal) and sonochemical irradiation (nanostructures).

Polyaniline-Coated TiO2 Nanorods for Photocatalytic Degradation of Bisphenol A in Water

Polyaniline (PANI)-wrapped TiO₂ nanorods (PANI/TiO₂), obtained through the oxidative polymerization of aniline at the surface of hydrothermally presynthesized TiO₂ nanorods, were evaluated as photocatalysts for the degradation of Bisphenol A (BPA). Fourier-transform infrared spectroscopy analysis revealed the successful incorporation of PANI into TiO₂ by the appearance of peaks at 1577 and 1502 cm^-1 that are due to the C=C and C-N stretch of the benzenoid or quinoid ring in PANI. Brunauer-Emmett-Teller analysis revealed that PANI/TiO₂ had almost double the surface area of TiO₂ (44.8999 m²/g vs 28.2179 m²/g). Transmission electron microscopy (TEM) analysis showed that TiO₂ nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO₂ nanorods. X-ray photon spectroscopy survey scan of the PANI/TiO₂ nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including pH, contact time, dosage, and initial concentration of BPA, was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using the 0.2 g/L PANI/TiO₂ photocatalyst at pH 10. The quantum yield (QY) of these photocatalysts was evaluated to be 9.86 × 10^-5 molecules/photon and 2.82 × 10^-5 molecules/photon for PANI/TiO₂ and TiO₂, respectively. PANI/TiO₂ showed better performance than as-synthesized TiO₂ with a rate constant of 4.46 × 10^-2 min^-1 compared to 2.18 × 10^-2 min^-1. The rate of degradation of PANI/TiO₂ was also superior to that of TiO₂ (150 mmol/g/h vs 74.89 mmol/g/h). Nitrate ions increased the rate of degradation of BPA, while humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1, and 93.1. The PANI/TiO₂ nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. LC-MS results revealed three possible BPA degradation intermediates. LC-MS analysis identified degradation products which included protonated BPA, [C₁₄H₁₃O₂ ⁺], and [C₉H₁₁O⁺]. The PANI/TiO₂ nanocomposite demonstrated superior photocatalytic activity with respect to improved QY and figure of merit and lower energy consumption.

Photocatalytic degradation of microcystin-LR by modified TiO2 photocatalysis: A review

Microcystin-LR (MC-LR), the most toxic and commonly encountered cyanotoxin, is produced by harmful cyanobacterial blooms and potentially threatens human and ecosystems health. Titanium dioxide (TiO₂) photocatalysis is attracting growing attention and has been considered as an efficient, environmentally friendly and promising solution to eliminate MC-LR in the aquatic ecosystems. Over recent decades, scientific efforts have been directed towards the understanding of fundamentals, modification strategies, and application potentials of TiO₂ photocatalysis in degrading MC-LR. In this article, recent reports have been reviewed and progress has been summarized in the development of heterogeneous TiO₂-based photocatalysts for MC-LR photodegradation under visible, UV, or solar light. The proposed photocatalytic principles of TiO₂ and destruction of MC-LR have been thoroughly discussed. Specifically, some main modification methods for improving the drawbacks and performance of TiO₂ nanoparticle were highlighted, including element doping, semiconductor coupling, immobilization, floatability amelioration and magnetic separation. Moreover, the performance evaluation metrics quantum yield (QY) and figure of merit (FOM) were used to compare different photocatalysts in MC-LR degradation. The best performance was seen in N-TiO₂ with QY and FOM values of 2.20E-07 molecules/photon and 1.00E-11 mol·L/(g·J·h). N-TiO₂ or N-TiO₂-based materials may be excellent options for photocatalyst design in terms of MC-LR degradation. Finally, a summary of the remaining challenges and perspectives on new tendencies in this exciting frontier and still an emerging area of research were addressed accordingly. Overall, the present review will offer a deep insight for understanding the photodegradation of MC-LR with modified TiO₂ to further inspire researchers that work in associated fields.

Gas Phase Photocatalytic CO2 Reduction, “A Brief Overview for Benchmarking”

Photocatalytic CO2 reduction is emerging as an affordable route for abating its ever increasing concentration. For commercial scale applications, many constraints are still required to be addressed. A variety of research areas are explored, such as development of photocatalysts and photoreactors, reaction parameters and conditions, to resolve these bottlenecks. In general, the photocatalyst performance is mostly adjudged in terms of its ability to only produce hydrocarbon products, and other vital parameters such as light source, reaction parameters, and type of photoreactors used are not normally given appropriate attention. This makes a comprehensive comparison of photocatalytic performance quite unrealistic. Hence, probing the photocatalytic performance in terms of apparent quantum yield (AQY) with the consideration of certain process and experimental parameters is a more reasonable and prudent approach. The present brief review portrays the importance and impact of aforementioned parameters in the field of gas phase photocatalytic CO2 reduction.