Highly selective CO₂ photoreduction to CO on MOF-derived TiO₂

Metal–Organic Framework (MOF)-derived TiO2, synthesised through the calcination of MIL-125-NH2, is investigated for its potential as a CO2 photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH4. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH4. Over the range of experimental settings explored, the MOF-derived TiO2 displays high selectivity towards CO (98%), with only a small amount of CH4 (2%) being produced. This is notable when compared to other state-of-the-art TiO2 based CO2 photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO2 was found to have a peak production rate of 8.9 × 10−4 μmol cm−2 h−1 (2.6 μmol g−1 h−1) and 2.6 × 10−5 μmol cm−2 h−1 (0.10 μmol g−1 h−1) for CO and CH4, respectively. A comparison is made to commercial TiO2, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10−3 μmol cm−2 h−1 (5.9 μmol g−1 h−1), but a lower selectivity preference for CO (3 : 1 CH4 : CO) than the MOF-derived TiO2 material developed here. This paper showcases the potential for MIL-125-NH2 derived TiO2 to be further developed as a highly selective CO2 photoreduction catalyst for CO production

Systematic study of TiO2/ZnO mixed metal oxides for CO2 photoreduction

A two component three degree simplex lattice experimental design was employed to evaluate the impact of different mixing ratios of TiO2 and ZnO on an ordered mesoporous SBA-15 support for CO2 photoreduction. It was anticipated that their combined advantages: low cost, non-toxicity and combined electronic properties would facilitate CO2 photoreduction. The ratio of TiO2 used had a statistically significant positive impact on CO (b1 = 9.71, p-value = 2.9310–4) and CH4 (b1 = 1.43, p-value = 1.3510–3) cumulative production. A negative impact, from the interaction term between the ratios of TiO2 and ZnO, was found for CH4 cumulative production (b3 = -2.64, p-value = 2.3010–2). The systematic study provided evidence for the possible loss in CO2 photoreduction activity from sulphate groups. The decrease in activity is attributed to the presence of sulphate species in the ZnO prepared, which may possibly act as charge carrier and/or radical intermediate scavengers

Review of material design and reactor engineering on TiO2 photocatalysis for CO2 reduction

The continuous combustion of non-renewable fossil fuels and depletion of existing resources is intensifying the research and development of alternative future energy options that can directly abate and process ever-increasing carbon dioxide (CO2) emissions. Since CO2 is a thermodynamically stable compound, its reduction must not consume additional energy or increase net CO2 emissions. Renewable sources like solar energy provide readily available and continuous light supply required for driving this conversion process. Therefore, the use of solar energy to drive CO2 photocatalytic reactions simultaneously addresses the aforementioned challenges, while producing sustainable fuels or chemicals suitable for use in existing energy infrastructure. Recent progress in this area has focused on the development and testing of promising TiO2 based photocatalysts in different reactor configurations due to their unique physicochemical properties for CO2 photoreduction. TiO2 nanostructured materials with different morphological and textural properties modified by using organic and inorganic compounds as photosensitizers (dye sensitization), coupling semiconductors of different energy levels or doping with metals or non-metals have been tested. This review presents contemporary views on state of the art in photocatalytic CO2 reduction over titanium oxide (TiO2) nanostructured materials, with emphasis on material design and reactor configurations. In this review, we discuss existing and recent TiO2 based supports, encompassing comparative analysis of existing systems, novel designs being employed to improve selectivity and photoconversion rates as well as emerging opportunities for future development, crucial to the field of CO2 photocatalytic reduction. The influence of different operating and morphological variables on the selectivity and efficiency of CO2 photoreduction is reviewed. Finally, perspectives on the progress of TiO2 induced photocatalysis for CO2 photoreduction will be presented

Synthetic strategies to nanostructured photocatalysts for CO2 reduction to solar fuels and chemicals

Artificial photosynthesis represents one of the great scientific challenges of the 21st century, offering the possibility of clean energy through water photolysis and renewable chemicals through CO2 utilisation as a sustainable feedstock. Catalysis will undoubtedly play a key role in delivering technologies able to meet these goals, mediating solar energy via excited generate charge carriers to selectively activate molecular bonds under ambient conditions. This review describes recent synthetic approaches adopted to engineer nanostructured photocatalytic materials for efficient light harnessing, charge separation and the photoreduction of CO2 to higher hydrocarbons such as methane, methanol and even olefins

Improving CO2 photoconversion with ionic liquid and Co single atoms

Photocatalytic CO2 conversion promises an ideal route to store solar energy into chemical bonds. However, sluggish electron kinetics and unfavorable product selectivity remain unresolved challenges. Here, an ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate, and borate-anchored Co single atoms were separately loaded on ultrathin g-C3N4 nanosheets. The optimized nanocomposite photocatalyst produces CO and CH4 from CO2 and water under UV-vis light irradiation, exhibiting a 42-fold photoactivity enhancement compared with g-C3N4 and nearly 100% selectivity towards CO2 reduction. Experimental and theoretical results reveal that the ionic liquid extracts electrons and facilitates CO2 reduction, whereas Co single atoms trap holes and catalyze water oxidation. More importantly, the maximum electron transfer efficiency for CO2 photoreduction, as measured with in-situ μs-transient absorption spectroscopy, is found to be 35.3%, owing to the combined effect of the ionic liquid and Co single atoms. This work offers a feasible strategy for efficiently converting CO2 to valuable chemicals

Zn-Cr layered double hydroxides for photocatalytic transformation of CO2 under visible light irradiation: the effect of the metal ratio and interlayer anion

Carbon dioxide is the main gas responsible for the greenhouse effect. Over the last few years, the research focus of many studies has been to transform CO2 into valuable products (CO, HCOOH, HCHO, CH3OH and CH4), since it would contribute to mitigating global warming and environmental pollution. Layered double hydroxides (LDHs) are two-dimensional materials with high CO2 adsorption capacity and compositional flexibility with potential catalytic properties to be applied in CO2 reduction processes. Herein, Zn-Cr LDH-based materials with different metal ratio and interlayer anions, i.e., chloride (Cl−), graphene quantum dots (GQDs), sodium dodecyl sulfate (SDS) and sodium deoxycholate (SDC), have been prepared by a co-precipitation method and characterized by different techniques. The influence of the interlayer inorganic and organic anions and the metal ratio on the application of Zn-Cr LDHs as catalysts for the photocatalytic CO2 reduction reaction under visible light irradiation is unprecedentedly reported. The catalytic tests have been carried out with Ru(bpy)32+ as photosensitizer (PS) and triethanolamine as sacrificial electron donor (ED) at λ = 450 nm. All LDHs materials exhibited good photocatalytic activity towards CO. Among them, LDH3-SDC showed the best catalytic performance, achieving 10,977 µmol CO g−1 at 24 h under visible light irradiation with a CO selectivity of 88%. This study provides pertinent findings about the modified physicochemical features of Zn-Cr LDHs, such as particle size, surface area and the nature of the interlayer anion, and how they influence the catalytic activity in CO2 photoreduction

Reverse Semi-Combustion Driven by Titanium Dioxide-Ionic Liquid Hybrid Photocatalyst

EP/L015633/1 EP/K005138/1 CAPES (158804/2017/01-and 001 FAPERGS -16/2552-0000 18/2551-0000561-4 88887.195052/2018-00 CNPq :406260/2018-4 169462/2017-0 406750/2016-5 465454/2014-3 grant agreement No 810310Unprecedented metal-free photocatalytic CO2 conversion to CO (up to 228±48 μmol g−1 h−1) was displayed by TiO2@IL hybrid photocatalysts prepared by simple impregnation of commercially available P25-titanium dioxide with imidazolium-based ionic liquids (ILs). The high activity of TiO2@IL hybrid photocatalysts was mainly associated to (i) TiO2@IL red shift compared to the pure TiO2 absorption, and thus a modification of the TiO2 surface electronic structure; (ii) TiO2 with IL bearing imidazolate anions lowered the CO2 activation energy barrier. The reaction mechanism was postulated to occur via CO2 photoreduction to formate species by the imidazole/imidazole radical redox pair, yielding CO and water.publishersversionpublishe

Rationally designed transition metal hydroxide nanosheet arrays on graphene for artificial CO2 reduction

The performance of transition metal hydroxides, as cocatalysts for CO2 photoreduction, is significantly limited by their inherent weaknesses of poor conductivity and stacked structure. Herein, we report the rational assembly of a series of transition metal hydroxides on graphene to act as a cocatalyst ensemble for efficient CO2 photoreduction. In particular, with the Ru-dye as visible light photosensitizer, hierarchical Ni(OH)2 nanosheet arrays-graphene (Ni(OH)2-GR) composites exhibit superior photoactivity and selectivity, which remarkably surpass other counterparts and most of analogous hybrid photocatalyst system. The origin of such superior performance of Ni(OH)2-GR is attributed to its appropriate synergy on the enhanced adsorption of CO2, increased active sites for CO2 reduction and improved charge carriers separation/transfer. This work is anticipated to spur rationally designing efficient earth-abundant transition metal hydroxides-based cocatalysts on graphene and other two-dimension platforms for artificial reduction of CO2 to solar chemicals and fuels

SODIUM LAURETH SULFATE (SLS) DECORATED α-PbO NANOCRYSTALS: OPTICAL, STRUCTURE, AND MORPHOLOGY, PROPERTIES

SODIUM LAURETH SULFATE (SLS) DECORATED α-PbO NANOCRYSTALS: OPTICAL, STRUCTURE, AND MORPHOLOGY PROPERTIES. The α-PbO nanocrystals were successfully decorated using sodium laureth sulfate (SLS) anionic surfactant. The method used is one-pot synthesis approach. The precursor used is lead nitrate (Pb(NO3)2). The UV-Vis spectrophotometer showed the absorption peak of α-PbO nanocrystals was seen at wavelength of 237 nm and an absorbance value of 0.7. The optical properties of PbO nanocrystals can be seen at the bandgap value of 4.2 eV. FT-IR spectroscopy showed the shift of absorption peak at the wavenumber of 1358 cm-1. XRD spectroscopy showed the crystals of PbO at diffraction angles (2θ) of 10-80o: 29.17, 32.54, 37.85, 39.62, 45.16, 46.21, 56.12, and 61.73 with miller indices of (111), (200), (201), (121), (220), (030), (311), and (032), respectively. The crystal size average of PbO was 56.32 nm. The results of PSA and PZC shows the particle size distribution of PbO is 71.5 nm with inter-particle charge of -25 mV. SEM-EDX data shows the PbO nanocrystals have an irregularly spherical with a compounds composition of Pb (83.12%) and O (16.88%). From the data of characterization, it can be concluded the PbO nanocrystals was successfully decorated using the surfactant anionic of sodium laureth sulfate