SrTiO3@NiFe LDH core–shell composites for photocatalytic CO2 conversion

A series of core@shell SrTiO₃@NiFe LDH composites (STONFs) were synthesized and their photocatalytic CO₂ reduction performance was studied. The photocatalyst STONF 2 exhibited enhanced CO₂ reduction performance with CO yield of 7.9 μmol g⁻¹ h⁻¹. The yield was 25.7 times and 8.8 times higher than that of NiFe LDH and SrTiO₃ respectively, and also higher than most LDH based photocatalysts. Compared with two individual components, STONFs exhibited their combined merits of widened absorption spectrum, higher transportation efficiency and alleviated recombination of e⁻/h⁺ pairs. In addition, there were fewer oxygen vacancies in STONF 2 than as-prepared SrTiO₃. Lower oxygen vacancies concentration would increase the opportunity of direct bonding between interface atoms of two components and successively increase the electron transportation and separation. These factors synergistically contributed to enhanced photocatalytic performance. This work will provide new insight for designing complementary multi-component photocatalysis systems.

A series of core@shell SrTiO₃@NiFe LDH composites (STONFs) were synthesized and their photocatalytic CO₂ reduction performance was studied.     

Construction of a novel two-dimensional AgBiO3/BiOBr step-scheme heterojunction for enhanced broad-spectrum photocatalytic performance

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO₃ on BiOBr. The self-assembled hierarchical structure of AgBiO₃/BiOBr was formed from flower-like AgBiO₃ and plate-like BiOBr. The optimized AgBiO₃/BiOBr heterojunction possessed excellent visible-light photocatalytic degradation efficiency (83%) for ciprofloxacin (CIP) after 120 min, with 1.46- and 4.15-times higher activity than pure AgBiO₃ and BiOBr, respectively. Furthermore, the removal ratio of multiple organic pollutants including tetracycline, Rhodamine B, Lanasol Red 5B and methyl orange was also investigated. Environmental interference experiments demonstrated that high pollutant concentrations, low photocatalyst dose and the addition of ions (SO₄²⁻, PO₄³⁻, HPO₄²⁻, H₂PO₄⁻) inhibited the photocatalytic activities. Subsequently, a simultaneous degradation experiment showed the competitive actions between CIP and RhB for radicals, decreasing the photocatalytic activity of CIP. Furthermore, trapping and electron spin resonance experiments showed that h⁺ and ˙O₂⁻ played a certain role in the degradation process and that ˙OH acted as assistant.

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO₃ on BiOBr.     

Synthesis of SrTiO3 submicron cubes with simultaneous and competitive photocatalytic activity for H2O splitting and CO2 reduction

Single crystalline strontium titanate (SrTiO₃) submicron cubes have been synthesized based on a molten salt method. The submicron cubes showed superior photocatalytic activity towards both water splitting and carbon dioxide reduction, in which methane (CH₄) and hydrogen (H₂) were simultaneously produced. The average production rate of methane up to 8 h is 4.39 μmol g⁻¹ h⁻¹ but drops to 0.46 μmol g⁻¹ h⁻¹. However, the average production rate of hydrogen is 14.52 before 8 h but then increases to 120.23 μmol g⁻¹ h⁻¹ after 8 h. The rate change of the two processes confirms the competition between the H₂O splitting and CO₂ reduction reactions. Band structure and surface characteristics of the SrTiO₃ submicron cubes were characterized by diffuse reflective UV-Vis spectroscopy, Mott–Schottky analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results reveal that the simultaneous and competitive production of methane and hydrogen is due to a thermodynamics factor, as well as the competition between the adsorption of carbon dioxide and water molecules on the surface of the faceted SrTiO₃. This work demonstrates that SrTiO₃ photocatalysts are efficient in producing sustainable fuels via water splitting and carbon dioxide reduction reactions.

There is a clear competitive relationship between water splitting and photocatalytic reduction of carbon dioxide in the whole process of photocatalytic reduction of carbon dioxide with the prepared cubic SrTiO₃ as a photocatalyst.     

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst

Selective photocatalytic reduction of CO₂ has been regarded as one of the most amazing ways for re-using CO₂. However, its application is still limited by the low CO₂ conversion efficiency. This work developed a novel Pt/In₂O₃/g-C₃N₄ multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO₂ reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In₂O₃ and g-C₃N₄ acted as visible photocatalysts, in which porous g-C₃N₄ facilitated H₂ production from water splitting while the In₂O₃ nanosheets embedded in g-C₃N₄ pores favored CO₂ fixation and H adsorption onto the Lewis acid sites. Besides, the In₂O₃/g-C₃N₄ heterojunctions could efficiently inhibit the photoelectron–hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H₂ production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron–hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO₂ molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO₂ conversion was 63.1 μmol g⁻¹ h⁻¹ and could reach up to 736.3 μmol g⁻¹ h⁻¹ at 40 atm.

A multifunctional Pt/In₂O₃/g-C₃N₄ catalyst exhibited high activity and selectivity to HCOOH during CO₂ reduction owing to the synergy between visible-light harvesting, CO₂ activation, HER, and photoelectron–hole separation via heterojunctions.     

Hybrid BiOBr/UiO-66-NH2 composite with enhanced visible-light driven photocatalytic activity toward RhB dye degradation

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years. In this work, a highly active, visible light photocatalyst BiOBr/UiO-66-NH₂ hybrid composite was successfully prepared by introducing various amounts of UiO-66-NH₂ with BiOBr through a co-precipitation method. The composites were applied for the photocatalytic degradation of RhB (rhodamine B) dye. The developed BiOBr/UiO-66-NH₂ composites exhibited higher photocatalytic activity than the pristine material. In RhB degradation experiments the hybrid composite with 15 wt% of UiO-66-NH₂ shows degradation efficiency conversion of 83% within two hours under visible light irradiation. The high photodegradation efficiency of BUN-15 could be ascribed to efficient interfacial charge transfer at the heterojunction and the synergistic effect between BiOBr/UiO-66-NH₂. In addition, an active species trapping experiment confirmed that photo-generated hole⁺ and O₂⁻ radicals are the major species involved in RhB degradation under visible light.

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years.     

Visible-light photocatalytic performance,recovery and degradation mechanism of ternary magnetic Fe3O4/BiOBr/BiOI composite

The ternary magnetic Fe₃O₄/BiOBr/BiOI (x : 3 : 1) photocatalysts were successfully synthesized by a facile solvothermal method. The samples were characterized by XRD, SEM, EDS, ICP-AES, XPS, UV-vis DRS, PL and VSM. Nitrogen-containing dye RhB was used as a degradation substrate to evaluate the photocatalytic degradation activities of the samples. The photocatalytic performance of Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) is superior to other Fe₃O₄/BiOBr/BiOI (x : 3 : 1). Compared with binary magnetic Fe₃O₄/BiOBr (0.5 : 1) prepared in our previous work, the Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) has obvious advantages in photocatalytic activity and adsorption capacity. And the specific surface area (48.30 m² g⁻¹) is much larger than that of the previous report (Fe₃O₄/BiOBr/BiOI (0.5 : 2 : 2)) synthesized by a co-precipitation method. Besides, after 25 s of magnetic field, Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) can be rapidly separated from water. After eight recycling cycles, the magnetic properties, photocatalytic activity, crystallization and morphology of the Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) catalyst remain good. The possible photocatalytic degradation mechanism of RhB under Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) photocatalyst was also proposed. The results indicate that the ternary magnetic Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) composite with high photocatalytic degradation efficiency, good magnetic separation performance and excellent recyclability and stability has potential application prospect in wastewater.

The ternary magnetic Fe₃O₄/BiOBr/BiOI (x : 3 : 1) photocatalysts were successfully synthesized by a facile solvothermal method.     

Pt–Nix alloy nanoparticles: a new strategy for cocatalyst design on a CdS surface for photo-catalytic hydrogen generation

Solar photocatalytic water splitting for the production of hydrogen has been a core aspect for decades. A highly active and durable photocatalyst is crucial for the success of the renewable hydrogen economy. To date, the development of highly effective photocatalysts has been seen by the contemporary research community as a grand challenge. Thus, herein we put forward a sincere attempt to use a Pt–Ni_x alloy nanoparticle (NP) cocatalyst loaded CdS photocatalyst ((Pt–Ni_x)/CdS) for photocatalytic hydrogen production under visible light. The Pt–Ni_x alloy NP cocatalyst was synthesized using a one-pot solvothermal method. The cocatalyst nanoparticles were deposited onto the surface of CdS, forming a Pt–Ni_x/CdS photocatalyst. Photocatalytic hydrogen production was carried out using a 300 W Xe light equipped with a 420 nm cut-off filter. The H₂ evolution rate of the Pt–Ni₃/CdS photocatalyst can reach a value as high as 48.96 mmol h⁻¹ g⁻¹ catalyst, with a quantum efficiency of 44.0% at 420 nm. The experimental results indicate that this Pt–Ni₃/CdS photocatalyst is a prospective candidate for solar hydrogen generation from water-splitting.

In this report, PtNi_x alloy NPs coupled with a CdS photocatalyst for photocatalytic hydrogen generation under visible light have been explored.     

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH

Optimized photocatalytic conversion of CO₂ requires new potent catalysts that can absorb visible light. The photocatalytic reduction of CO₂ using rhenium(i) has been demonstrated but suffers from low turnover. Herein, we describe a [Re(CO)₃(1-(1,10)phenanthroline-5-(4-nitro-naphthalimide))Cl] photocatalyst, which when combined with the sacrificial donor 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, results in selective production of formic acid and a high turnover number of 533 and turnover frequency of 356 h⁻¹. Single-crystal X-ray diffraction and DFT studies are also discussed.

Rhenium based photocatalytic conversion CO₂ to formate in the visible region with excellent turnover.     

Synthesis and photocatalytic CO2 reduction performance of aminated coal-based carbon nanoparticles

To obtain high-efficiency, low-cost, environmentally friendly carbon-based photocatalytic material, we synthesized coal-based carbon dots with sp² carbon structure and multilayer graphene lattice structure by the hydrogen peroxide (H₂O₂) oxidation method to strip nano-scale crystalline carbon in the coal structure and link with oxygen-containing groups such as the hydroxyl group. N, S co-doped aminated coal-based carbon nanoparticles (NH₂-CNPs) were then obtained by thionyl chloride chlorination and ethylenediamine passivation. The physical properties and chemical structure of the synthesized NH₂-CNPs were studied and the photocatalytic CO₂ reduction performance was tested. The results show that NH₂-CNPs are vesicle-type spherical particles with particle size of 42.16 ± 7.5 nm and have a mesoporous structure that is capable of adsorbing CO₂. A defect structure was formed on the surface of the NH₂-CNPs due to the doping of N and S elements, thereby significantly improving the ability to photogenerate electrons under visible light along with the ability to efficiently separate the photo-generated carriers. The photocatalytic reduction products of CO₂ over NH₂-CNPs were CH₃OH, CO, C₂H₅OH, H₂ and CH₄. After 10 hours of reaction, the total amount of products was 807.56 μmol g⁻¹ cat, the amount of CH₃OH was 618.7 μmol g⁻¹ cat, and the calculated selectivity for conversion of CO₂ to CH₃OH was up to 76.6%.

Aminated coal-based carbon nanoparticles (NH₂-CNPs) was fabricated. The physical properties and chemical structure of the NH₂-CNPs was studied. Photocatalytic CO₂ reduction activity of NH₂-CNPs were measured and the reaction mechanism was discussed.     

BiOBr hybrids for organic pollutant removal by the combined treatments of adsorption and photocatalysis

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method. To determine the optimal formula, the photocatalytic degradation of C. I. reactive red 2 (X3B) with xSiO₂–BiOBr (x = 0–5) was investigated. Under simulated sunlight irradiation, 4SiO₂–BiOBr exhibited a better photocatalytic efficiency than other materials; 1.77 and 1.51 times higher than conventional nano TiO₂ and pure BiOBr, respectively. To demonstrate the photocatalytic degradation mechanism, the effect of active species on degradation of X3B was carried out, and a possible degradation pathway was proposed. To realize the combined treatments of adsorption and photocatalysis, an inorganic/organic (I/O) SN–SiO₂–BiOBr hybrid was further strategized and synthesized. It showed much better adsorption performance than the SiO₂–BiOBr composite. It could enrich organic pollutants by facile adsorption, and then degrade them to H₂O and CO₂ under natural sunlight irradiation. Notably, this sunlight-driven photocatalysis can be performed in the slurry resulted from the pollutant adsorption. As a result, the proposed combination of adsorption and photocatalysis will provide a novel strategy to greatly facilitate the treatment of organic wastewater.

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method.     

Covalent organic framework with sulfonic acid functional groups for visible light-driven CO2 reduction

In this study, a covalent organic framework (TpPa–SO₃H) photocatalyst with sulfonic acid function groups was synthesized using a solvothermal method. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, N₂ adsorption–desorption measurements, and field emission scanning electron microscopy. An electrochemical workstation was used to test the photoelectric performance of the materials. The results show that TpPa–SO₃H has –SO₃H functional groups and high photocatalytic performance for CO₂ reduction. After 4 h of visible-light irradiation, the amount of CO produced is 416.61 μmol g⁻¹. In addition, the TpPa–SO₃H photocatalyst exhibited chemical stability and reusability. After two testing cycles under visible light irradiation, the amount of CO produced decreased slightly to 415.23 and 409.15 μmol g⁻¹. The XRD spectra of TpPa–SO₃H were consistent before and after the cycles. Therefore, TpPa–SO₃H exhibited good photocatalytic activity. This is because the introduction of –SO₃H narrows the bandgap of TpPa–SO₃H, which enhances the visible light response range and greatly promotes the separation of photogenerated electrons.

In this study, covalent organic framework (TpPa–SO₃H) photocatalyst with sulfonic acid function groups was synthesized using a solvothermal method.     

MOF-5 derived carbon as material for CO2 absorption

In our study we prepared MOF-5 derived carbon to reveal the thermodynamics of CO₂ absorption processes in great detail. Porous carbon material was prepared from a metal–organic framework (MOF-5) via carbonization at 1000 °C. The obtained structure consists only of carbon and exhibits a BET specific surface area, total pore volume and micropore volume of 1884 m² g⁻¹, 1.84 cm³ g⁻¹ and 0.59 cm³ g⁻¹, respectively. Structural analysis allowed the assumption that this material is an ideal candidate for efficient CO₂ absorption. The CO₂ uptake was 2.43 mmol g⁻¹ at 25 °C and 1 bar. Additionally, the absorption over a wide range of temperatures (25, 40, 60, 80 and 100 °C) and pressures (in range of 0–40 bar) was investigated. It is shown that the CO₂ absorption isotherm fits a multitemperature Sips model. The calculated Sips equation parameters allows the isosteric heat of adsorption to be obtained. The isosteric heat of adsorption for CO₂ decreased substantially with an increase in surface coverage by gas molecules. This indicates a negligible intermolecular interaction between CO₂ molecules. A decrease in the isosteric heat of adsorption with surface coverage is a result of the disappearance of favourable adsorption sites.

In our study we prepared MOF-5 derived carbon to reveal the thermodynamics of CO₂ absorption processes in great detail.     

Rational design direct Z-scheme BiOBr/g-C3N4 heterojunction with enhanced visible photocatalytic activity for organic pollutants elimination

A rapid recombination of photo-generated electrons and holes, as well as a narrow visible light adsorption range are two intrinsic defects in graphitic carbon nitride (g-C₃N₄)-based photocatalysts. Inspired by natural photosynthesis, an artificially synthesized Z-scheme photocatalyst can efficaciously restrain the recombination of photogenerated electron–hole pairs and enhance the photoabsorption ability. Hence, to figure out the above problems, BiOBr/g-C₃N₄ composite photocatalysts with different mass ratios of BiOBr were successfully synthesized via a facile template-assisted hydrothermal method which enabled the BiOBr microspheres to in situ grow on the surface of g-C₃N₄ flakes. Furthermore, to explore the origin of the enhanced photocatalytic activity of BiOBr/g-C₃N₄ composites, the microstructure, photoabsorption ability and electrochemical property of BiOBr/g-C₃N₄ composites were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS) and photocurrent (PC) response measurements. As a result, the introduction of BiOBr on g-C₃N₄ to constitute a direct Z-scheme heterojunction system can effectively broaden the light absorption range and promote the separation of photo-generated electron–hole pairs. Hence, compared with pure g-C₃N₄ and BiOBr, the resultant BiOBr/g-C₃N₄ composites exhibit the remarkable activity of photodegradated rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) under visible light irradiation. Simultaneously, the optimal BiOBr content of the BiOBr/g-C₃N₄ composites was obtained. The BiOBr/g-C₃N₄ composites exhibit an excellent photostability and reusability after four recycling runs for degradation RhB. Moreover, the active-group-trapping experiment confirmed that ·OH, ·O₂⁻ and h⁺ were the primary active groups in the degradation process. Based on the above research results, a rational direct Z-scheme heterojunction system is contrastively analyzed and proposed to account for the photocatalytic degradation process of BiOBr/g-C₃N₄ composites.

The morphology, electrochemical property, photoabsorption ability and photocatalytic activity of BiOBr/g-C₃N₄ composites are discussed. A rational photocatalytic mechanism is proposed.     

Photochemical conversion of CO2 to CO by a Re complex: theoretical insights into the formation of CO and HCO3− from an experimentally detected monoalkyl carbonate complex

Triethanolamine (TEOA) has been used for the photocatalytic reduction of CO₂, and the experimental studies have demonstrated that the TEOA increases the catalytic efficiency. In addition, the formation of a carbonate complex has been confirmed in the Re photocatalytic system where DMF and TEOA are used as solvents. In this study, we survey the reaction pathways of the photocatalytic conversions of CO₂ to CO + H₂O and CO₂ to CO + HCO₃⁻ by fac-Re(bpy)(CO)₃Br in the presence of TEOA using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster approach, DLPNO-CCSD(T). Under light irradiation, the solvent-coordinated Re complex is first reduced to form a monoalkyl carbonate complex in the doublet pathway. This doublet pathway is kinetically advantageous over the singlet pathway. To reduce carbon dioxide, the Re complex needs to be reduced by two electrons. The second electron reduction occurs after the monoalkyl carbonate complex is protonated. The second reduction involves the dissociation of the monoalkyl carbonate ligand, and the dissociated ligand recombines the Re center via carbon to generate Re–COOH species, which further reacts with CO₂ to generate tetracarbonyl complex and HCO₃⁻. The two-electron reduced ligand-free Re complex converts CO₂ to CO and H₂O. The pathways leading to H₂O formation have lower barriers than the pathways leading to HCO₃⁻ formation, but their portion of formation must depend on proton concentration.

DFT and DLPNO-CCSD(T) calculations proposed a pathway for the conversion of the experimentally detected monoarkyl carbonate complex to tetracarbonyl complex.     

Electrospun metal and metal alloy decorated TiO2 nanofiber photocatalysts for hydrogen generation

Photocatalytic nanofibers of TiO₂ decorated with 2% metal (Pt, Pd, and Cu) and metal alloys (Pt₂Pd and PtCu) were synthesized by the polymer-assisted electrospinning method, followed by microwave-assisted ethylene glycol reduction. Structurally, nanofibers calcined at 500 °C adopted an anatase phase along with a remnant rutile phase. Morphological, structural, and photocatalytic studies were carried out using scanning and transmission electron microscopy equipped with an energy dispersive spectroscopy attachment, X-ray powder diffraction, X-ray photoelectron spectroscopy, and photocatalytic hydrogen generation under UV-Vis irradiation. The calcined nanofibers were found to have a diameter of 60.0 ± 5.0 nm and length of up to several microns. High resolution TEM imaging suggests that the nanofibers are composed of agglomerated individual TiO₂ nanoparticles, which are tightly packed and stacked along the axial direction of the nanofibers. PXRD studies suggest alloy formation, as evident from peak shifting towards higher two-theta values. Surface modification with co-catalysts is shown to contribute considerably to the rate of photocatalytic H₂ generation. The amount of H₂ generated gradually increases as a function of time. The 2%Pt₂Pd/TiO₂ catalyst shows the highest rate of H₂ generation (4 mmol h⁻¹ gram_catalyst), even higher than that of 2%Pt/TiO₂ nanofiber photocatalyst (2.3 mmol h⁻¹ gram_catalyst), while 2%Cu/TiO₂ nanofiber photocatalyst shows the least activity among the decorated catalysts (0.04 mmol h⁻¹ gram_catalyst).

Photocatalytic hydrogen generation by electrospun TiO₂ nanofibers decorated with various co-catalysts (Pt₂Pd, PtCu, Cu, Pt, Pd) was explored.     

An amine-bifunctionalization strategy with Beta/KIT-6 composite as a support for CO2 adsorbent preparation

An amine-bifunctionalized composite strategy was used to fabricate grafted-impregnated micro-/mesoporous composites for carbon dioxide capture. The micro-/mesoporous Beta/KIT-6 (BK) composite containing a high-silica zeolite with a three-dimensional twelve-membered ring crossing channel system and cubic structural silica was used as a support, and 3-aminopropyltrimethoxysilane (APTS) and tetraethylenepentamine (TEPA) were used as the grafted and impregnated components, respectively. The amine efficiency, adsorption kinetics, thermal stability, regeneration performance, and the effects of impregnated amine loadings (30–60%) and temperatures (40–90 °C) on the CO₂ adsorption performance were investigated using a thermal gravimetric analyzer (TGA) in the mixed gases (15 vol% CO₂ and 85 vol% N₂). At 60 °C, the bifunctionalized Beta/KIT-6 (1 mL APTS g⁻¹ BK) displayed the highest CO₂ adsorption capacity of 5.12 mmol g⁻¹ at a TEPA loading of 50%. The kinetic model fitting results showed that the CO₂ adsorption process was a combination of physical and chemical adsorption, wherein the chemical adsorption is dominant. After five adsorption/desorption cycle regenerations, the saturated adsorption capacity of the composite material was 4.86 mmol g⁻¹, which was only 5.1% lower than the original adsorption capacity. The composites demonstrated excellent CO₂ adsorption performance, indicating the promising future of these adsorbents for CO₂ capture from actual flue gas after desulfurization.

CO₂ adsorption curves of A-BK-TEPA-50 at 40, 60, 75, 80 and 90 °C.     

Deposition of platinum on boron-doped TiO2/Ti nanotube arrays as an efficient and stable photocatalyst for hydrogen generation from water splitting

An efficient photocatalyst of boron-doped titanium dioxide/titanium nanotube array-supported platinum particles (Pt–B/TiO₂/Ti NTs) was fabricated for photocatalytic water splitting for hydrogen production through a two-step route. First, B/TiO₂/Ti NTs were prepared by anodic oxidation using hydrofluoric acid as electrolyte and boric acid as a B source. Then, Pt particles were deposited on the surface of B/TiO₂/Ti NTs by photo-assisted impregnation reduction. The structure and properties of Pt–B/TiO₂/Ti NTs were characterized by various physical measurements which showed the successful fabrication of Pt–B/TiO₂/Ti NTs. The Pt–B/TiO₂/Ti NTs, with a B-doping content of 15 mmol L⁻¹, showed the highest photocatalytic activity and exhibited a photocatalytic hydrogen-production rate of 384.9 μmol g⁻¹ h⁻¹, which was 9.2-fold higher than that of unmodified TiO₂/Ti NTs (41.7 μmol g⁻¹ h⁻¹). This excellent photocatalytic performance was ascribed mainly to the synergistic effect of Pt and B, which could enhance the photocatalytic activity of TiO₂/Ti NTs.

Pt–B/TiO₂/Ti NTs, prepared by anodic oxidation and photo-deposition methods, showed excellent photocatalytic activity.     

CdSe/ZIF-8-x: synthesis and photocatalytic CO2 reduction performance

The photocatalytic reduction of CO₂ is an effective way to solve the greenhouse effect. Different kinds of materials, such as semiconductors, coordination compounds, and bioenzymes, have been widely investigated to increase the efficiency of the photocatalytic reduction of CO₂. However, a high selectivity and great stability are still challenges for material scientists. Here, we report for the first time visible light photocatalytic CO₂ reduction by a series of CdSe/ZIF-8 nanocomposites combining the excellent CO₂ adsorption capacity of ZIF-8 and the narrow energy gap of CdSe quantum dots (QDs). The composites show a higher catalytic performance than those of the pure components. Among CdSe/ZIF-8-x (x = n_CdSe/n_ZIF-8), the highest yield (42.317 μmol g⁻¹) for reducing CO₂ to CO in 12 h, was obtained using nanocomposites with a ratio of 0.42 (n_CdSe/n_ZIF-8) within the range of investigation.

CdSe/ZIF-8-x combines the excellent CO₂ adsorption capacity of ZIF-8 and the narrow energy gap of CdSe to show an enhanced CO₂ photoreduction performance.

Nowadays, global energy shortage and environmental pollution are two major obstacles to the development of human society, and have attracted increasing concern. Using solar energy to convert CO₂ into valuable fuels or chemicals is extremely attractive due to its dual function of the reduction of the greenhouse effect and also as an alternative energy source to fossil fuels. Recently, different kinds of materials, such as semiconductor materials,^1–3 metal complexes,^4–6 and bioenzyme catalysts,⁷ have been explored for photocatalytic CO₂ reduction.Metal–organic frameworks (MOFs) constructed from metal-containing clusters and organic building blocks are types of crystalline porous materials, and have been widely applied in many fields, such as gas storage,⁸ electrochemical energy storage (EES)^9,10 and catalysis.¹¹ Recently, MOFs^12–14 have been considered as potential new catalysts due to their excellent capability for CO₂ adsorption and capture.¹⁵ These porous materials provide a large number of catalytic active sites, and their porous structures are conducive to charge transfer.¹⁶ During the adsorption process, CO₂ coordinates with unsaturated metal sites and forms chemical bonds with MOFs.¹² Blom and co-workers demonstrated that CO₂ can interact with metal ions and form end-on adducts with one of the oxygen lone pair orbitals.¹⁷ZIF-8, which is constructed from Zn²⁺ centres and imidazolate ligands, shows a high CO₂ adsorption capacity since the imidazolate ligand has a high adsorption capacity for CO₂ and also a strong complexation ability of CO₂.¹⁸ However, ZIF-8 has a wide band gap (4.9 eV, ref. 19), which means that ZIF-8 is barely photoactive enough to catalyse CO₂ reduction. However, CdSe QDs can easily be excited to generate electron–hole pairs upon visible light irradiation due to their narrow band gap. Osterloh and co-workers reported CdSe QDs of several sizes applied to photocatalytic H₂ evolution and showed the quantitative relationship between the degree of quantum confinement and the photocatalytic H₂ evolution.²⁰In this work, we synthesized a series of CdSe/ZIF-8-x composites, which combine the excellent CO₂ adsorption capacity of ZIF-8 with the narrow energy gap of CdSe QDs. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) indicated the successful combination of CdSe QDs and ZIF-8. The CdSe/ZIF-8 composite exhibits an increased yield for reducing CO₂ to CO compared with pure CdSe QDs or ZIF-8. Under visible light irradiation for 12 h, the CO yield was 42.317 μmol g⁻¹, which is 6.13 and 10.84 times the yields catalysed by CdSe (6.901 μmol g⁻¹) and by ZIF-8 (3.905 μmol g⁻¹), respectively.Reagents used in this work were analytically pure and used without further purification. Powder X-ray diffraction (PXRD) analysis was performed using a Rigaku Dmax-2000 diffractometer equipped with a Cu Kα (λ = 0.15406 nm) radiation source. The morphology of the catalysts was observed by transmission electron microscopy (TEM, JEOL JEM-2100F) operated at 200 kV. Scanning electron microscopy (SEM) pictures were prepared using a Hitachi scanning electron microscope S-4800. Elemental mapping was carried out by energy dispersive X-ray spectroscopy (EDS) on the same instrument. Inductively coupled plasma spectrometry (ICP, Cary5000) was used for multi-elemental analyses. The CO₂ absorption behaviours of the catalysts were studied with physical adsorption apparatus (ASAP 2020M). Solid UV-visible diffuse reflectance spectroscopy (UV-vis DRS) was carried out at room temperature to evaluate the band gap energy (E_g). The products of the photocatalytic CO₂ reduction were detected by gas chromatography (GC7900, Techcomp). Dynamic light scattering (DLS) measurements were carried out on an Elitesizer from Brookhaven.CdSe QDs were synthesized by a previously reported procedure.²¹ The resulting CdSe QDs were precipitated by adding ethanol and dispersed in 5 mL of hexane as a stock solution.The synthesis of CdSe/ZIF-8 was based on the pure ZIF-8 synthesis process with modification.²² A certain quantity of the above CdSe QD stock solution was precipitated by adding ethanol, and re-dispersed in 5 mL of an n-hexanol solution of 0.1642 g (2 mmol) of 2-methylimidazole (Hmim) via ultrasonication. A solution of Zn(NO₃)₂·6H₂O (0.074 g, 0.25 mmol) in 5 mL of n-hexanol was rapidly poured into the above solution under stirring. The product was collected by centrifugation after 1 h, washed with n-hexanol twice and dried at 80 °C for 12 h under vacuum. The samples produced from n_Cd²⁺/n_Zn²⁺ equal to 0.4, 0.8, and 1.2 were named as samples 1 to 3, respectively.The photocatalytic CO₂ reduction performance of CdSe/ZIF-8-x was performed in a typical catalytic system with [Ru(bpy)₃]²⁺ (bpy = 2′,2-bipyridine) as a photosensitizer and triethanolamine (TEOA) as a sacrificial reducing agent in CO₂-saturated acetonitrile (MeCN).^23–27 The photosensitizer [Ru(bpy)₃]Cl₂·6H₂O (2 mg) and catalysts CdSe/ZIF-8-x (5 mg) were dispersed in a solution of 1 mL of triethanolamine (TEOA) and 4 mL of acetonitrile. Before irradiation, the suspension was purged with CO₂ for 15 min to eliminate any air. With vigorous stirring, a 300 W Xe lamp with a 420 nm cut-off filter was utilized as the light source. After illumination for 12 h, the produced gases were analysed and quantified by gas chromatography.The molar ratios of CdSe to ZIF-8 of the composites were characterized by ICP (

NaYF4:Yb,Tm@TiO2 core@shell structures for optimal photocatalytic degradation of ciprofloxacin in the aquatic environment

The removal of antibiotic residues in the aquatic environment is still a big challenge in environmental protection. Here, we developed NaYF₄:Yb,Tm@TiO₂ as a highly efficient photocatalyst for photocatalytic degradation of ciprofloxacin (CIP), a representative antibiotic in water under simulated solar irradiation. NaYF₄:Yb,Tm@TiO₂ can efficiently utilize a broad spectrum of solar energy to improve the efficiency of ciprofloxacin removal from an aquatic environment. The optimum operation conditions of photocatalyst dosage, pH value, and initial concentrations of CIP were determined by a series of contrast experiments. The dynamic process of CIP removal was monitored by UV-vis spectrophotometry, and can be well predicted by a pseudo first order model. The optimal conditions of photocatalyst dosage, initial concentration of CIP and pH value for CIP photocatalytic degradation were 1 g L⁻¹, 10⁻⁵ M and 8, respectively. This study provides an efficient method for antibiotic removal and enables a promising strategy for other organic water pollutant treatments.

The study indicated the optimum operation conditions to effectively remove ciprofloxacin from aquatic environment by NaYF₄:Yb,Tm@TiO₂ structures.     

Novel BiOBr by compositing low-cost biochar for efficient ciprofloxacin removal: the synergy of adsorption and photocatalysis on the degradation kinetics and mechanism insight

C/BiOBr composite materials were synthesized via a simple one-step solvothermal method, with C derived from biochar, which was prepared from the low-cost straw. The samples were characterized by SEM, XRD, XPS and PL. The 2% C/BiOBr composite material showed a noticeable adsorption and photocatalysis synergistic effect to remove CIP. The adsorption rate and degradation rate were 1.45 times and 1.8 times that of BiOBr. The adsorption kinetics and isotherms of CIP on C/BiOBr were analyzed with the pseudo-second-order kinetic and Langmuir models. The degradation efficiency was 96.8% after 60 min of irradiation. High stability and degradability were still maintained after four cycles. The Bi–O–C bond accelerated electron transition and inhibited the rapid photogenerated electron pair recombination. In the degradation process of CIP, ˙O₂⁻ and h⁺ played a significant role. Experiments proved that C/BiOBr is practical and feasible for the degradation of CIP under the synergistic effect of adsorption and photocatalysis.

1. The C-loaded BiOBr was synthesized via a one-step solvothermal method. 2. C/BiOBr showed an obvious synergistic effect of adsorption and photocatalysis on the degradation of ciprofloxacin.