Photocatalytic reduction of CO2 over Ti3+ self-doped TiO2-based nanomaterials

In this study, we explored the photocatalytic efficacy of Ti3+-doped TiO2-based photocatalysts for CO2 reduction. The Ti3+ self-doped photocatalysts were synthesized using a straightforward chemical reduction with sodium borohydride (NaBH4). Our investigation aimed to elucidate the intricate interplay between the synthesis process and the quantity of NaBH4 reductant on the physical-chemical and photocatalytic attributes of the defective TiO2-based photocatalysts. We explored three different commercially available TiO2 materials labeled P25, (S)TiO2, and KRONOClean7050, which were reduced (2 g of TiO2) with 0.75 and 1.5 g of NaBH4. The reduction with 0.75 g of NaBH4 led to a significant decrease of photocatalytic activity in all three cases. It was caused by clogging of the photocatalysts surface by sodium ions which resulted in the surface recombination of charge carriers. Oppositely, the reduction with 1.5 g of NaBH4, led to an increase of the photocatalytic activity with superior performance of KRONOClean7050. The comprehensive characterization of all the samples explained this superior performance of KC7050_RED_1.5 sample. Importantly, it did not contain any amorphous phase and the crystal size was two times higher compared to other 2 samples reduced by 1.5 g of NaBH4. In the addition to higher crystallinity, the formation of a disordered TiO2−x layer, enriched with Ti3+ defects and oxygen vacancies, was confirmed. These structural features enhance the light absorption and mitigate undesired recombination of photogenerated charge carriers. These results would trigger farther investigation of defect engineering towards enhancement of the efficiency of metal oxide photocatalysts.European Union's Horizon 2020 project SAN4Fuel, (101079384, HORIZON-WIDERA-2021-ACCESS-03–01); European Commission, EC, (101120397, CZ.10.03.01/00/22_003/0000048, HORIZON-WIDERA-2022-TALENTS, RRC/12/2022); Grantová Agentura České Republiky, GA ČR, (GA CR 21-24268K); Narodowe Centrum Badań i Rozwoju, NCBR, (NOR/POLNORCCS/PhotoRed/0007/2019-00)Large Research Infrastructure ENREGAT [LM2023056]; Norway Grants 2014-2021 via the National Centre for Research and Development [NOR/POLNORCCS/PhotoRed/0007/2019-00]; Czech Science Foundation [GA CR 21-24268K]; European Union [HORIZON-WIDERA-2021-ACCESS-03-01: 101079384, CZ.10.03.01/00/22_003/0000048]; Support for Science and Research in the Moravia- Silesia Region 2022 [RRC/12/2022]; APPROACH [101120397

Influence of rGO and Preparation Method on the Physicochemical and Photocatalytic Properties of TiO2/Reduced Graphene Oxide Photocatalysts

In this study, a series of TiO2/rGO photocatalysts were obtained with a two-step procedure: a solvothermal method and calcination at 300–900 °C in an argon atmosphere. It was noted that the presence of rGO in photocatalysts had an important role in the changes in crystallite size and specific surface area. In TiO2/rGO samples, different surface functional groups, such as C−Cgraph, C−Caliph, C−OH, C=O, and CO(O), were found. It was observed that rGO modification suppressed the anatase-to-rutile phase transformation. The photocatalytic activity of the obtained nanomaterials was investigated through the decomposition of methylene blue under UV and artificial solar light irradiation. It was found that the adsorption degree played an important role in methylene blue decomposition. The experimental results revealed that TiO2/rGO samples exhibited superior removal efficiency after calcination for methylene blue compared toTiO2 without rGO, as well as a commercial photocatalyst KRONOClean 7000. It was noted that photocatalytic activity increased with the increase in the calcination temperature. The highest activity was observed for the sample calcined at 700 °C, which consisted of 76% anatase and 24% rutile. This study clearly demonstrated that TiO2/rGO samples calcined in argon can be used as efficient photocatalysts for the application of methylene blue decomposition

Assessment of the Suitability of the One-Step Hydrothermal Method for Preparation of Non-Covalently/Covalently-Bonded TiO2/Graphene-Based Hybrids

A hybrid nanocomposites containing nanocrystalline TiO2 and graphene-related materials (graphene oxide or reduced graphene oxide) were successfully prepared by mechanical mixing and the hydrothermal method in the high-pressure atmosphere. The presented X-ray photoelectron spectroscopy (XPS) study and quantitative elemental analysis confirm similar content of carbon in graphene oxide GO (52 wt% and 46 wt%, respectively) and reduced graphene oxide rGO (92 wt% and 98 wt%, respectively). No chemical interactions between TiO2 and GO/rGO was found. TiO2 nanoparticles were loaded on GO or rGO flakes. However, Fourier transform infrared-diffuse reflection spectroscopy (FTIR/DRS) allowed finding peaks characteristic of GO and rGO. XPS study shows that since the concentration of TiO2 in the samples was no less than 95 wt%, it was assumed that the interactions between TiO2 and graphene should not influence the lower layers of titanium atoms in the TiO2 and they occurred as Ti4+ ions. Hydrothermal treatment at 200 °C did not cause the reduction of GO to rGO in TiO2-GO nanocomposites. In general, the one-step hydrothermal method must be considered to be inefficient for preparation of chemically-bonded composites synthesized from commercially available TiO2 and unfunctionalized graphene sheets obtained from graphite powder

TiO Supported on Quartz Wool for Photocatalytic Oxidation of Hydrogen Sulphide

A spacial system consisting of TiO 2 on a fibrous support was prepared by hydrolysis of titanium isopropoxide in the presence of quartz wool, followed by calcination. The material was characterized by X-ray diffraction, nitrogen adsorption–desorption at 77 K, X-ray photoelectron spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The TiO 2 /support system was examined as a photocatalyst for UV-assisted oxidation of H 2 S in air. The results obtained confirmed a superior performance of the TiO 2 /support system over TiO 2 powder. H 2 S underwent oxidation to elemental sulphur and/or S 6+ . The relative amounts of these species were influenced by humidity

Surface characteristics of KOH-treated commercial carbons applied for CO adsorption

The effect of an alkali treatment (potassium hydroxide) on the properties of a commercial activated carbon has been studied. The aim of the treatment was to improve the adsorption properties of the material toward carbon dioxide. In the result of the treatment, silica contained in the raw carbon was removed and the density of the material increased. The changes in the surface chemistry were observed as well. The treatment of the activated carbon with KOH resulted in a complete removal of carboxy and lactone groups and a decrease of the general content of the acidic groups (more significant than that of basic groups). Simultaneously, the surface concentration of hydroxyl groups increased. The alkali treatment of activated carbon resulted in an increase of carbon dioxide uptake of 14% (measured using a volumetric method at 0℃). The adsorption of carbon dioxide on activated carbon has a mixed (physicochemical) character and that two types of adsorption sites are present at the surface. The adsorption energy varies roughly from 25 to 60 kJ/mol

Photocatalytic reduction of CO2 over Ti3+ self-doped TiO2-based nanomaterials

In this study, we explored the photocatalytic efficacy of Ti3+-doped TiO2-based photocatalysts for CO2 reduction. The Ti3+ self-doped photocatalysts were synthesized using a straightforward chemical reduction with sodium borohydride (NaBH4). Our investigation aimed to elucidate the intricate interplay between the synthesis process and the quantity of NaBH4 reductant on the physical-chemical and photocatalytic attributes of the defective TiO2-based photocatalysts. We explored three different commercially available TiO2 materials labeled P25, (S)TiO2, and KRONOClean7050, which were reduced (2 g of TiO2) with 0.75 and 1.5 g of NaBH4. The reduction with 0.75 g of NaBH4 led to a significant decrease of photocatalytic activity in all three cases. It was caused by clogging of the photocatalysts surface by sodium ions which resulted in the surface recombination of charge carriers. Oppositely, the reduction with 1.5 g of NaBH4, led to an increase of the photocatalytic activity with superior performance of KRONOClean7050. The comprehensive characterization of all the samples explained this superior performance of KC7050_RED_1.5 sample. Importantly, it did not contain any amorphous phase and the crystal size was two times higher compared to other 2 samples reduced by 1.5 g of NaBH4. In the addition to higher crystallinity, the formation of a disordered TiO2−x layer, enriched with Ti3+ defects and oxygen vacancies, was confirmed. These structural features enhance the light absorption and mitigate undesired recombination of photogenerated charge carriers. These results would trigger farther investigation of defect engineering towards enhancement of the efficiency of metal oxide photocatalysts

Predictive performance of multi-model ensemble forecasts of COVID-19 across European nations

Background: Short-term forecasts of infectious disease burden can contribute to situational awareness and aid capacity planning. Based on best practice in other fields and recent insights in infectious disease epidemiology, one can maximise the predictive performance of such forecasts if multiple models are combined into an ensemble. Here, we report on the performance of ensembles in predicting COVID-19 cases and deaths across Europe between 08 March 2021 and 07 March 2022. Methods: We used open-source tools to develop a public European COVID-19 Forecast Hub. We invited groups globally to contribute weekly forecasts for COVID-19 cases and deaths reported by a standardised source for 32 countries over the next 1–4 weeks. Teams submitted forecasts from March 2021 using standardised quantiles of the predictive distribution. Each week we created an ensemble forecast, where each predictive quantile was calculated as the equally-weighted average (initially the mean and then from 26th July the median) of all individual models’ predictive quantiles. We measured the performance of each model using the relative Weighted Interval Score (WIS), comparing models’ forecast accuracy relative to all other models. We retrospectively explored alternative methods for ensemble forecasts, including weighted averages based on models’ past predictive performance. Results: Over 52 weeks, we collected forecasts from 48 unique models. We evaluated 29 models’ forecast scores in comparison to the ensemble model. We found a weekly ensemble had a consistently strong performance across countries over time. Across all horizons and locations, the ensemble performed better on relative WIS than 83% of participating models’ forecasts of incident cases (with a total N=886 predictions from 23 unique models), and 91% of participating models’ forecasts of deaths (N=763 predictions from 20 models). Across a 1–4 week time horizon, ensemble performance declined with longer forecast periods when forecasting cases, but remained stable over 4 weeks for incident death forecasts. In every forecast across 32 countries, the ensemble outperformed most contributing models when forecasting either cases or deaths, frequently outperforming all of its individual component models. Among several choices of ensemble methods we found that the most influential and best choice was to use a median average of models instead of using the mean, regardless of methods of weighting component forecast models. Conclusions: Our results support the use of combining forecasts from individual models into an ensemble in order to improve predictive performance across epidemiological targets and populations during infectious disease epidemics. Our findings further suggest that median ensemble methods yield better predictive performance more than ones based on means. Our findings also highlight that forecast consumers should place more weight on incident death forecasts than incident case forecasts at forecast horizons greater than 2 weeks. Funding: AA, BH, BL, LWa, MMa, PP, SV funded by National Institutes of Health (NIH) Grant 1R01GM109718, NSF BIG DATA Grant IIS-1633028, NSF Grant No.: OAC-1916805, NSF Expeditions in Computing Grant CCF-1918656, CCF-1917819, NSF RAPID CNS-2028004, NSF RAPID OAC-2027541, US Centers for Disease Control and Prevention 75D30119C05935, a grant from Google, University of Virginia Strategic Investment Fund award number SIF160, Defense Threat Reduction Agency (DTRA) under Contract No. HDTRA1-19-D-0007, and respectively Virginia Dept of Health Grant VDH-21-501-0141, VDH-21-501-0143, VDH-21-501-0147, VDH-21-501-0145, VDH-21-501-0146, VDH-21-501-0142, VDH-21-501-0148. AF, AMa, GL funded by SMIGE - Modelli statistici inferenziali per governare l'epidemia, FISR 2020-Covid-19 I Fase, FISR2020IP-00156, Codice Progetto: PRJ-0695. AM, BK, FD, FR, JK, JN, JZ, KN, MG, MR, MS, RB funded by Ministry of Science and Higher Education of Poland with grant 28/WFSN/2021 to the University of Warsaw. BRe, CPe, JLAz funded by Ministerio de Sanidad/ISCIII. BT, PG funded by PERISCOPE European H2020 project, contract number 101016233. CP, DL, EA, MC, SA funded by European Commission - Directorate-General for Communications Networks, Content and Technology through the contract LC-01485746, and Ministerio de Ciencia, Innovacion y Universidades and FEDER, with the project PGC2018-095456-B-I00. DE., MGu funded by Spanish Ministry of Health / REACT-UE (FEDER). DO, GF, IMi, LC funded by Laboratory Directed Research and Development program of Los Alamos National Laboratory (LANL) under project number 20200700ER. DS, ELR, GG, NGR, NW, YW funded by National Institutes of General Medical Sciences (R35GM119582; the content is solely the responsibility of the authors and does not necessarily represent the official views of NIGMS or the National Institutes of Health). FB, FP funded by InPresa, Lombardy Region, Italy. HG, KS funded by European Centre for Disease Prevention and Control. IV funded by Agencia de Qualitat i Avaluacio Sanitaries de Catalunya (AQuAS) through contract 2021-021OE. JDe, SMo, VP funded by Netzwerk Universitatsmedizin (NUM) project egePan (01KX2021). JPB, SH, TH funded by Federal Ministry of Education and Research (BMBF; grant 05M18SIA). KH, MSc, YKh funded by Project SaxoCOV, funded by the German Free State of Saxony. Presentation of data, model results and simulations also funded by the NFDI4Health Task Force COVID-19 (https://www.nfdi4health.de/task-force-covid-19-2) within the framework of a DFG-project (LO-342/17-1). LP, VE funded by Mathematical and Statistical modelling project (MUNI/A/1615/2020), Online platform for real-time monitoring, analysis and management of epidemic situations (MUNI/11/02202001/2020); VE also supported by RECETOX research infrastructure (Ministry of Education, Youth and Sports of the Czech Republic: LM2018121), the CETOCOEN EXCELLENCE (CZ.02.1.01/0.0/0.0/17-043/0009632), RECETOX RI project (CZ.02.1.01/0.0/0.0/16-013/0001761). NIB funded by Health Protection Research Unit (grant code NIHR200908). SAb, SF funded by Wellcome Trust (210758/Z/18/Z)