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In this study, we assessed the effect of the incorporation of multi-walled carbon nanotubes (MWCNT) on a TiO2 support containing different active metals to obtain Metal/TiO2-MWCNT photocatalytic systems. The materials prepared in this work were characterized by ICP-OES, TEM, EDX, XRD, PL, UV–vis, and nitrogen physisorption techniques. Among those investigated metals, Cu was shown to be the most promising for the present application. The assessment of the photocatalytic performance of Cu/TiO2-MWCNT with various Cu contents revealed that the catalytic activity depends on the Cu loading and the photocatalyst with 1 wt.% of Cu displayed the best performance among investigated. The incorporation of MWCNT in the support enhanced the photocatalytic activity towards the production of H2 under visible and UV–vis light irradiation at room temperature. The authors thank Ministerio de Ciencia Innovación y Universidades and FEDER (Project RTI2018-095291-B-I00) and the Generalitat Valenciana (PROMETEOII/2018/076) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079). MNG gratefully acknowledges Generalitat Valenciana and Plan GenT (CDEIGENT/2018/027) for the postdoctoral grant. The present work was partially supported by Grants-in-Aid for Scientific Research (Nos. 26220911, 19H00838) from the Japan Society for the Promotion of Science (JSPS) and MEXT. KM, YK, and HY thank MEXT program “Elements Strategy Initiative to Form Core Research Center.

Different photocatalysts based on the combination of TiO2 and CuxO have been prepared by simple and reproducible procedures. The synthesized systems have been applied in the photoreduction of CO2 to yield CH4 inside a 2-dimensional flow reactor in which the gas stream was passed over a thin layer of the catalyst under UV irradiation. Analysis of the photocatalysts reveals that the oxidation state of Cu changes throughout the reaction, thus modifying the physicochemical properties of the catalysts. The combination of core-level and valence-band level spectroscopies allowed us to draw the band diagram for the best catalyst, showing a Z-scheme structure. The reactor design and the photocatalyst developed can produce CH4 at a very high production rate with extreme efficiency. After further optimization through suppression of side reactions, we obtained one of the highest values reported for any type of reactor or catalytic system with a CH4 formation rate over 100 μmolCH4·gcat−1 h−1 using low power LED lighting. The authors thank the Generalitat Valenciana (PROMETEOII/2018/076) for financial support. MNG gratefully acknowledges Generalitat Valenciana and Plan GenT (CDEIGENT/2018/027) for the postdoctoral grant.

An efficient gas-phase production of propylene oxide (PO) with noble metal-free catalysts could modify the industrial output of this valuable compound. We present a novel catalyst based on well-dispersed Ni nanoparticles loaded on a Ti-SiO2 support for the propylene epoxidation reaction using H2/O2 mixtures. XPS, High Resolution Transmission Electron Microscopy (HRTEM), and UV–Vis corroborate both the small size of Ni particles and the excellent dispersion and incorporation of Ti as tetrahedral single site species into the silica framework. The catalytic results under steady-state conditions at low temperature (200 °C) show high PO selectivity (around 85%) with a substantial propylene conversion (over 6%) and excellent H2 efficiency (~37%) using only 0.5 wt% of Ni on Ti-SiO2 (Ti/Si = 0.01 M ratio). In this work, we have also carried out a preliminary DFT study to gain understanding of the characteristics that make this nickel catalyst active and selective for the propene epoxidation reaction. We thank the Spanish Ministry of Economy and Competitiveness (MINECO), Spanish Ministry of Science, Innovation and Universities, Generalitat Valenciana and FEDER (CTQ2015-66080-R, RTI2018-095291-B-I00, MAT2017-87579-R, and PROMETEO/2018/076) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079).

In this work, we reported the preparation of composites based on titania (TiO2) and Zeolite Socony Mobil-5 (ZSM-5) nanozeolite, following two approaches (i.e., incorporating the presynthesized zeolite in the synthesis medium of TiO2 and incorporating presynthesized TiO2 in the synthesis medium of ZSM-5). The materials synthesized were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectrometry analysis, and their photocatalytic activities were assessed in the oxidation of propene in the gas phase. It was observed that the synthesis methodology affects the final properties of the composite, which ultimately affected their photocatalytic performance in the studied application. It was found that the Nano-ZSM5/TiO2 composite was the most active among the investigated samples, which was attributed to the intimate contact between the two components of the composite, the preserved properties of the photocatalytic active phase in the final material, and the positive contribution of the nanozeolite by increasing the local concentration of propene. The authors thank Ministerio de Ciencia Innovación y Universidades and FEDER (Project RTI2018-095291-B-I00) and the Generalitat Valenciana (PROMETEOII/2018/076) for financial support. J.F.-C. thanks MINECO for a researcher formation grant (BES-2016-078079). M.N.-G. gratefully acknowledges Generalitat Valenciana and Plan GenT (CDEIGENT/2018/027) for the postdoctoral grant.

This work constitutes a guide towards the preparation of metal-organic framework materials (MOF) supported and/or confined in activated carbon monoliths (ACM). The resulting hybrid porous materials exhibit improved physico-chemical properties as compared with their parent constituents. The different hybrids were obtained exploring several experimental approaches, which were thoroughly discussed. All hybrids were characterized by N2 adsorption isotherms, SEM, TGA and XRD techniques. The characterization studies pointed out that the preparation conditions are of paramount importance in defining the nucleation and growth of HKUST-1, either outside of the carbon grains (surface coating), and/or in the internal pores (bulk confinement). While the surface coating was achieved by directly synthesizing the MOF in presence of the ACM (i.e. in-situ synthesis), bulk confinement is favored after applying an additional step that involves a pre-nucleation at low temperatures (5 °C). The hybrid material with the best performance, sample A5(1), shows enhanced mechanical properties compared to its parent counterparts, combined with high apparent surface area (up to 1300 m2/g), an improved crushing strength (about 8 times superior to ACM) and a geometrical density of around 0.45 cm3/g, which almost duplicates that of ACM. Last but not least, the adsorption behavior of the hybrid was tested for CO2 and CH4 adsorption. Application of IAST equation to the single component adsorption isotherms at room temperature gives rise to a CO2/CH4 selectivity factor of 5.5 in the hybrid material, larger than that on ACM (S = 3.5). This work was supported by MINECO projects: MAT2013-45008-p. MEC wants to thank the Spanish Government for the fellowship FPU AP2010-4920.

In this study, we present a photo-microreactor illuminated with a low power LED light as a highly efficient system to achieve the total oxidation of propene using a TiO2 photocatalyst. This abatement system (photo-microreactor) consists in an immobilized benchmark photocatalyst (TiO2, P25) inside a commercial glass microchannel chip (UV transparent microfluidic chips, internal volume of 9.5 μl) using a packed-bed configuration without any previous treatment. The P25 inside the microreactor shows a nearly homogenous filling of the particles resulting in a low pressure drop throughout the system. In terms of propene abatement (Catalytic activity), the P25 inside the commercial microreactor reaches total propene conversion (100%) under flow conditions at low concentrations (100 ppmv) due to shorter diffusion distances, large surface-to-volume ratios, efficient heat transfer, and the improved light penetration inside the microchannel. Moreover, the prepared microreactor uses a low consumption power (LED), low residence time and presents a relatively low pressure drop making this device (P25 inside a commercial microreactor) very interesting for the abatement of volatile organic compounds at low concentration for example at indoor ambient due to its small size (45 × 15 mm). The acknowledgements come at the end of an article after the conclusions and before the notes and references. The authors thank MINECO (Project CTQ2015-66080-R, MINECO/FEDER) and the Generalitat Valenciana (PROMETEOII/2018/076) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079).

We have performed the synthesis of TiO2-MWCNT composites focusing on the distribution of the photoactive phase on the carbon active sites existing in the MWCNTs, and its effect on the properties of the composites for the abatement of propene. We have used different approaches for the dispersion of MWCNTs during the synthesis; 1) an ultrasound bath for 5 minutes, 2) an ultrasound bath for 60 minutes, and 3) an ultrasound probe for 5 min. We observed that the incorporation of MWCNTs in the TiO2 synthesis improves the catalytic activity in the photooxidation of propene, but the best results are obtained for ultrasound probe treatment. A good dispersion of the MWCNT and an increase in the active surface area or surface oxygen functionalities of the MWCNTs are key factors to achieve improved photocatalytic activity for total propene oxidation, thus benefitting from the synergy between TiO2 and MWCNT. The authors thank Ministerio de Ciencia Innovación y Universidades and FEDER (Project RTI2018-095291-B-I00) and the Generalitat Valenciana (PROMETEOII/2018/076) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079).

The elimination of volatile organic compounds (VOCs) at low concentration is a subject of great interest because these compounds are very harmful for the environment and human health. In this work, we have developed an easy methodology to immobilize a benchmark photocatalyst (P25) inside a capillary microreactor (Fused silica capillary with UV transparent coating) without any previous treatment. For this purpose, a dispersion of the sample (P25) in EtOH was used obtaining a packed bed configuration. We have improved the immobilization of the benchmark photocatalyst (P25) inside the capillary incorporating a surfactant (F-127) to generate porosity inside the microreactor to avoid severe pressure drops (∆P &lt, 0.5 bar). The resulting capillaries were characterized by Scanning Electron Microscopy (SEM). These microreactors show a good performance in the abatement of propene (VOC) under flow conditions per mol of active phase (P25) due to an improved mass transfer when the photocatalyst is inside the capillary. Moreover, the prepared microreactors present a higher CO2 production rate (mole CO2/(mole P25&middot, s)) with respect to the same TiO2 operating in a conventional reactor. The microreactor with low pressure drop is very interesting for the abatement of the VOCs since it improves the photoactivity of P25 per mol of TiO2 operating at near atmospheric pressure.

In this work, we have performed the encapsulation of a reference TiO2 material (P25) in spherical silica with hierarchical porosity using a sol-gel methodology. The same P25 material has been encapsulated within a “classical” MCM-41 mesoporous silica and a precipitated silica. The materials synthesized in this work were characterized by ICP-OES, SEM, TEM, EDX, XRD, UV–VIS, TG, and nitrogen adsorption. It has been observed that the P25 samples encapsulated in silica present improved CO2 production rates per mol of P25 in the photooxidation of propene, compared to P25 alone as well as the physical mixture of the two components. Moreover, the sample with a low content of P25 encapsulated in silica with hierarchical porosity presents the highest CO2 production rates per mol of P25 with respect to the other P25/silica samples, due to a better accessibility of the titania phase and improved illumination of the active phase. Furthermore, the hierarchical porosity of the silica shell material favours mass transport and an increased concentration of reagents by adsorption near the titania phase. This improvement in photocatalytic activity is obtained by following a simple and reproducible synthesis methodology that employs an established silica preparation protocol. Thus, the choice of a silica with an adequate porosity for this application is proven to be a promising advancement in the development of efficient photocatalysts. The authors thank MINECO (Project CTQ2015-66080-R, MINECO/FEDER) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079).

Despite the vast number of publication dealing with ZIF-8, the performance of this zeolitic MOF upon adsorption is still a matter of debate. The understanding of its adsorption properties its of great importance to define its potential in aplications such as gas separation, sensing and catalytic processes. Using inelastic neutron scattering (INS) upon exposure to different probe molecules we get further insight about the adsortion performance at cryogenic temperatures, including the possible swinging of the imidazolate linkers. The authors acknowledge financial support from the MINECO projects MAT-2013-45008-P, MAT2016-81732-ERC. EVRF gratefully acknowledge support from MINECO for his Ramón y Cajal grant (RyC-2012-11427) and University of Alicante for the project GRE-13-31. Generalitat Valenciana is acknowledge for support (PROMETEOII/2014/004). This research benefited from use of the VISION beamline (IPTS-15878.1) at ONRL’s Spallation Neutron Source and the VirtES (Virtual Experiments in Spectroscopy) project, (LDRD 7739), which are supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC.

One of the main concerns in the technological application of several metal–organic frameworks (MOFs) relates to their structural instability under pressure (after a conforming step). Here we report for the first time that mechanical instability can be highly improved via nucleation and growth of MOF nanocrystals in the confined nanospace of activated carbons. Financial support from MINECO projects MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) is gratefully acknowledged.

The elimination of volatile organic compounds (VOCs) at low concentration is a subject of great interest because these compounds are very harmful for the environment and human health. In this work, we have developed a synthesis methodology of TiO2 that allows obtaining meso-macroporous materials with hierarchical porosity and with high thermal stability for their application as photocatalysts in the removal of VOCs, specifically propene. The materials synthesized in this work were characterized by Scanning electron microscope (SEM), Transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Thermogravimetric Analysis (TG), and nitrogen adsorption. It is observed that the samples calcined at 250 °C and 500 °C present a high photoactivity for the photooxidation of propene, which is similar to the benchmark material P25 (commercial TiO2). Moreover, the textural properties are better than those for P25, indicating that the samples are interesting for the preparation of photocatalysts with different conformations, such as in the form of coatings and fillings in different size scales. The authors thank MINECO (CTQ2015-66080-R, MINECO/FEDER, BES-2016-078079) and Generalitat Valenciana (PROMETEOII/2014/010) for financial support.

Despite great attention toward transition metal tellurates especially M3TeO6 (M = transition metal) in magnetoelectric applications, control on single phasic morphology-oriented growth of these tellurates at the nanoscale is still missing. Herein, a hydrothermal synthesis is performed to synthesize single-phased nanocrystals of two metal tellurates, i.e., Ni3TeO6 (NTO with average particle size ∼37 nm) and Cu3TeO6 (CTO ∼ 140 nm), using NaOH as an additive. This method favors the synthesis of pure NTO and CTO nanoparticles without the incorporation of Na at pH = 7 in MTO crystal structures such as Na2M2TeO6, as it happens in conventional synthesis approaches such as solid-state reaction and/or coprecipitation. Systematic characterization techniques utilizing in-house and synchrotron-based characterization methods for the morphological, structural, electronic, magnetic, and photoconductivity properties of nanomaterials showed the absence of Na in individual particulate single-phase MTO nanocrystals. Prepared MTO nanocrystals also exhibit slightly higher antiferromagnetic interactions (e.g., TN-NTO = 57 K and TN-CTO = 68 K) compared to previously reported MTO single crystals. Interestingly, NTO and CTO show not only a semiconducting nature but also photoconductivity. The proposed design scheme opens the door to any metal tellurates for controllable synthesis toward different applications. Moreover, the photoconductivity results of MTO nanomaterials prepared serve as a preliminary proof of concept for potential application as photodetectors. Authors thank European Union-Next Generation EU, MINECO, and University of Alicante for a postdoctoral research grant (MARSALAS21-09), Jenny and Antti Wihuri Foundation, ERC (European Research Council) Starting Grant project UNIFY (grant agreement number 101039110), and Consolidator Grant CATCH (grant agreement no. 101002219).

Photocatalysis represents a promising technology that might alleviate the current environmental crisis. One of the most representative photocatalysts is graphitic carbon nitride (g-C3N4) due to its stability, cost-effectiveness, facile synthesis procedure, and absorption properties in visible light. Nevertheless, pristine g-C3N4 still exhibits low photoactivity due to the rapid recombination of photo-induced electron-hole (e−-h+) pairs. To solve this drawback, Z-scheme photocatalysts based on g-C3N4 are superior alternatives since these systems present the same band configuration but follow a different charge carrier recombination mechanism. To contextualize the topic, the main drawbacks of using g-C3N4 as a photocatalyst in environmental applications are mentioned in this review. Then, the basic concepts of the Z-scheme and the synthesis and characterization of the Z-scheme based on g-C3N4 are addressed to obtain novel systems with suitable photocatalytic activity in environmental applications (pollutant abatement, H2 production, and CO2 reduction). Focusing on the applications of the Z-scheme based on g-C3N4, the most representative examples of these systems are referred to, analyzed, and commented on in the main text. To conclude this review, an outlook of the future challenges and prospects of g-C3N4-based Z-scheme photocatalysts is addressed. This research was funded by European Union-Next Generation EU, MINECO, and University of Alicante: MARSALAS21-09, Generalitat Valenciana: CDEIGENT/2018/027, University of Alicante: GRE20-19-A. PID2021-123079OB-I00 project funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, European Union’s Horizon 2020 research and innovation programme: Grant Agreement 101002219 and Generalitat Valenciana: Proyecto Prometeo CIPROM/2021/70.