Surface Heterostructures Research Articles

TiO2-Based Catalysts with Various Structures for Photocatalytic Application: A Review

TiO2-based catalysts with various surface heterostructures (0D, 1D, 2D, and 3D) have been widely researched owing to their cost-effectiveness, high stability, and environmentally friendly nature, and can be used for many applications in various fields, including hydrogen production and pollutant degradation. However, there are also many existing problems limiting their practical application, such as their large band gap and rapid electron–hole recombination rate. Owing to the abundance of recent achievements in materials science, we will summarize the recent structural engineering strategies which provide favorable photocatalytic activity enhancements, such as enhanced visible light absorption, stability, an increased charge–carrier separation rate and improved specific surface area. Among the various structural engineering methods in this review, we will introduce TiO2-based materials with different dimensional structures. Meanwhile, we also discuss recent achievements in synthesis methods and application of TiO2-based catalysts in various fields. We aim to display a comprehensive overview which can be a guide for the development of a new generation of TiO2-based catalysts according to their structural design for enhanced solar energy conversion.

Rational heterostructure stacking enables 23% wide-bandgap perovskite solar cells by side-reaction inhibition

Suppressing side reactions led to the formation of rational Dion–Jacobson 2D/3D surface heterostructures, achieving an optimal PCE of 23.05% (certified 22.58%) for 1.68 eV perovskite solar cells.

MoS2/MoO3 heterojunctions enabled by surface oxidization of MoS2 nanosheets for high-performance room-temperature NO2 gas sensing

Transition-metal dichalcogenides (TMDs) have emerged as ideal candidates for room-temperature gas sensing due to their remarkable semiconductor properties. However, bare TMDs typically exhibit drawbacks such as low sensitivity, slow response, and low recovery speeds, which limit their applicability. In comparison to single materials, enhancing the sensing performance of the material can be achieved through the realization of heterostructures. Therefore, the key to improving the performance of metal-sulfide gas sensors lies in the controlled construction of unique heterostructures. In this work, surface heterostructures composed of molybdenum disulfide (MoS2) nanoflowers loaded with molybdenum trioxide (MoO3) enabled are realized through the surface oxidization of MoS2 nanosheets for high-performance room-temperature detection of NO2 gas. The heterostructures were easily constructed by oxidizing flower-like MoS2 using a hydrogen peroxide aqueous solution. The gas sensor based on the MoS2/MoO3 heterojunction exhibits a response of 18.9 % to 1 ppm NO2, which is nine times higher than that of the MoS2 sensor (2.1 %). Furthermore, even at a NO2 concentration as low as 50 ppb, the sensor response can reach 6.9 %. The sensor displays good repeatability and excellent selectivity. The enhanced gas-sensing performance of the MoS2/MoO3 heterostructure may result from the unique structure of MoS2 and the p-n heterojunction formed at the interfaces. The proposed design strategy and the surface heterostructure constructed in this work can provide guidance for the development of high-performance gas-sensitive materials and devices.

Nano Surface‐Heterogeneities of Particles Modulate the Macroscopic Properties of Hydrogels

AbstractNanoparticles, when incorporated into polymer matrices, can improve the intrinsic properties of composite materials. These materials possess fascinating properties and find widespread applications in bioengineering, medicine, aerospace, and electronics. However, the impact of nanoparticle surface heterostructures on composite systems is not fully understood. To bridge this gap, composite hydrogels (HRCs) are developed using rough‐surfaced raspberry‐like colloidal (RC) particles. It is hypothesized that the surface roughness of nanoparticles can significantly affect their adsorption, motion, and interfacial forces when interacting with polymeric networks, thereby influencing the macroscopic properties of HRCs. The properties of HRCs are compared with those of composite hydrogels containing smooth‐surfaced particles (HSCs) to isolate the effect of surface roughness. The results show that the nano‐surface heterogeneities of nanoparticles dictate the macroscopic properties of HRC hydrogels. It is found that HRCs exhibit much greater mechanical and adhesive properties compared to HSCs and control hydrogel without nanoparticles. As identified by the relaxation behavior, the enhanced frictional drag of interstitial fluid due to surface roughness, combined with the strong interaction of polymer network components dynamically linked by rough‐surfaced RC particles, is responsible for these improvements. These findings can guide the design and fabrication of new nanocomposites, including hydrogels, for various applications.

Acousto-optical coupling in two-dimensional air-slot phoxonic crystal heterostructure cavity

Phoxonic crystal is a periodic artificial structure that can manipulate optical and acoustic waves in the same temporal and spatial domain. It has broad application prospect in optical communication, optical mechanics sensor, quantum computations, phoxonic crystal integrated devices and so on. In this paper, we adopt a silicon-based two-dimensional square lattice structure, which can exhibit wide band gap of phonons and photons simultaneously. Then a periodic rectangular structure is introduced on the surface, the effects of the height and width of the rectangle on the optical and acoustic surface wave modes are analyzed. Based on the mode gap effect, a surface heterostructure composed of rectangles with different heights and widths is constructed. Then two identical surface heterostructures are placed face to face with an air slot in the middle, and connected with silicon substrate on both sides, which form an air slot heterostructure cavity. Five phononic cavity modes and three photonic cavity modes are obtained, the acousto-optical coupling rates between phononic and photonic cavity modes are calculated. The results show that the coupling rate between phononic and photonic cavity mode with the same symmetry and maximum overlap is the largest, and the coupling rates between the combination of phononic cavity modes α and β and photonic cavity modes can be adjusted by changing the phase difference φ of modes α and β. In this paper, the finite element method is used to simulate the calculation.

Construction of 2D/2D MoS2/g-C3N4 Heterostructures for Photoreduction of Cr (VI).

2D/2D MoS2/g-C3N4 (MCN) surface heterostructures were created by second thermal polymerization of bulk g-C3N4 and the reaction of thiourea and MoO3 at 670 °C. MoS2 networks grew vertically along the (002) facet on superior thin g-C3N4 nanosheets. The layered heterostructures drastically improved the Cr(VI) removal ability. In the dark case, 27% of Cr(VI) was removed within 45 min. The result indicates that the adsorption of Cr(VI) was a chemical adsorption process involving the sharing and transfer of electrons. The equilibrium data indicate that the adsorbent was covered with a monolayer adsorbate, which conformed to the Langmuir isotherm model (R2 = 0.9618). In addition, MCN nanocomposites could convert Cr(VI) into non-toxic Cr(III) by photoreduction under visible light irradiation. With an optimized composition, 100% of Cr(VI) was removed within 30 min, which was ∼10 times quicker compared with Cr(VI) removal under dark conditions. Because g-C3N4 nanosheets (sample CN670) with higher photocurrent density revealed the lowest photoreduction Cr(VI) ability, adsorption plays an important role in Cr(VI) removal. For MoS2/g-C3N4 nanocomposites used in Cr(VI) removal, adsorption and photoreduction were incorporated together to get excellent performance.

Surface Processes in Photocatalytic Reduction of CO2 on TiO2-based Materials

Owing to its excellent photoactivity, good stability and low cost, TiO<sub>2</sub> is one of the most studied semiconductor materials to convert CO<sub>2</sub> into useful chemicals, contributing to mitigate global warming. In this review, starting from the basic kinetic and thermodynamic principles of CO<sub>2</sub> photoreduction, the focus is on the surface processes involved in its capture and subsequent reactivity on TiO<sub>2</sub>. In particular, the role of different TiO<sub>2</sub> morphologies, facets and surface heterostructures is discussed. The effect of relevant co-adsorbed molecules (e.g., H<sub>2</sub>O) on the CO<sub>2</sub> reaction pathways is also considered. Moreover, the coupling of TiO<sub>2</sub> with graphene and metal nanoparticles to enhance the reaction rates is presented. A deeper understanding at the atomic level of these surface mechanisms could help the design of TiO<sub>2</sub>-based photocatalysts with improved efficiency and selectivity.

Layer-by-layer growth of molecular self-assembled monolayers /sputtered gold thin films/graphene oxide on glass substrate

In the present study, 1-dodecanethiol self-assembled monolayers (SAMs) on graphene oxide (GO) –Au (Gold) thin films as molecular templates for the selective deposition of multilayer films was performed. Thus, heterostructured GO/Au/DDT and DDT/Au/GO thin film are fabricated by sputtering Au target onto modified GO structure or self-assembled 1-dodecanethiol (DDT) arrays. It has been shown that a new device concept can be made by completing the glass substrate with the surface heterostructures; i.e. layer GO sheet or DDT with Au nanoparticles (Au NPs). In the light of the performed study, the layer-by-layer assembling of DDT on the GO sheet-Au thin films template has been proved for the distinct conjugation. Also, Optical and morphological characterizations are coherent with the instantaneous nucleation and growth model over the modified DDT-Au NPs-GO or GO-Au NPs-DDT thin films in the aspect of surface roughness, the phonon transport, and other multilayer films properties. As a consequence, the multilayer films of DDT-capped Au thin films and GO sheets have shown a better hybrid nanostructure with higher consistency, hierarchy and surface area. In addition, this work will present a new perspective for template preparation based on nanostructured thin films due to its unique properties resulting from nanoscale properties.

Photocatalytic Behaviors of TiO2 Nanoblets Coated with MoS2 Nanosheets for Solar‐Driven Photocatalysis

AbstractTiO2 nanoblets coated with MoS2 nanosheets, donated as T@M, were successfully prepared by a facile hydrothermal method. In comparison with pristine TiO2 nanoblets, the composite of MoS2 nanosheets could enlarge the spectral response of sunlight. The surface heterostructures of T@M nanocomposite could effectively separate the photogenerated electron‐hole pairs, and greatly inhibit the recombination of photogenerated electrons and holes. The photocatalytic performances of the as‐synthesized products were investigated in contrast by photodegradation of methylene blue, methyl orange, rhodamine B and levofloxacin. Under 350 W Xe lamp irradiating for 2 h, T@M exhibited excellent degradation performance. Interestingly, blue shifts of the dyes’ absorption peaks were observed, which probably attributed to the incomplete products decomposed by as‐absorbed dye molecules on the surface of TiO2 nanoblets. Compared with pure TiO2 nanoblets, T@M has less amount TiO2, higher separation efficiency of photogenerated electron‐hole pairs and better inhibition efficiency of photogenerated carriers’ recombination, leading less blue shift and higher degradation efficiency.

Synergistic effects of CuO and Au nanodomains on Cu2O cubes for improving photocatalytic activity and stability

Cu2O is a promising photocatalyst, but it suffers from poor photocatalytic activity and stability, especially for Cu2O cubes. Herein, we report the deposition of CuO and Au nanodomains on Cu2O cubes to form dual surface heterostructures (HCs) to improve photocatalytic activity and stability. The apparent quantum efficiency of Au/CuO/Cu2O HCs was ca. 123 times that of pristine Cu2O. In addition, the Au/CuO/Cu2O HCs maintained nearly 80% of its original activity after eight cycles in contrast to five cycles for the Au/Cu2O material. Therefore, CuO and Au domains greatly improved the photocatalytic activity and stability of the Cu2O cubes due to the synergistic effect of the HCs.

ZIF-8 derived hexagonal-like α-Fe2O3/ZnO/Au nanoplates with tunable surface heterostructures for superior ethanol gas-sensing performance

A series of hexagonal-like α-Fe2O3/ZnO/Au nanoplate heterostructures with tunable morphologies and superior ethanol gas-sensing performance were successfully synthesized via the facile multi-step reaction processes. Hexagonal-like α-Fe2O3 nanoplates with uniform size around 150 nm are employed as new sensor substrates for loading the well-distributed ZnO and Au nanoparticles with adjustable size distribution on the different surfaces. Brunauer-EmmeQ-Teller (BET) surface areas of α-Fe2O3 and α-Fe2O3/ZnO samples are evaluated to be 37.94 and 61.27 m2/g, respectively, while α-Fe2O3/ZnO/Au composites present the highest value of 79.08 m2/g. These α-Fe2O3-based functional materials can exhibit outstanding sensing properties to ethanol. When the ethanol concentration is 100 ppm, the response value of α-Fe2O3/ZnO/Au composites can reach up to 170, which is 14.6 and 80.3 times higher than that of α-Fe2O3/ZnO and pure α-Fe2O3, respectively. The recycling stability and long-time effectiveness can be availably maintained within 30 days, as well as the response and recovery times are shortened to 4 and 5 s, respectively. Significantly, the response value of α-Fe2O3/ZnO/Au composite is still up to 63 at an operating temperature of 280 °C even though the ethanol concentration decreases to 10 ppm. The enhanced gas sensing mechanism would be focused on the synergistic effects of phase compositions, surface heterogeneous structures, large specific surface area, and the selective depositions of Au nanoparticles in α-Fe2O3/ZnO/Au sensors. The synergistic effect of different surface heterostructures referring to α-Fe2O3/Au and α-Fe2O3/ZnO/Au and their novel electron transport processes on the surfaces are first investigated and discussed in details. It is expected that hexagonal-like α-Fe2O3/ZnO/Au nanoplate heterostructures with excellent sensing performance can be the promising highly-sensitive materials in the actual application for monitoring and detecting ethanol.

Construction of High Activity Titanium Dioxide Crystal Surface Heterostructures and Characterization of Its Basic Properties

Heterogeneous photocatalytic materials, which combine the advantages of photocatalytic materials and heterojunction, have been developed rapidly in the field of environmental pollution control. In this paper, TiO2 surface heterojunction catalysts with different catalytic activity were prepared by controlling the amount of HF, and their XRD characterization was also carried out. In addition, the optimum amount of HF was determined by photocatalytic degradation of simulated dye wastewater by methylene blue solution. And the optimal amount of catalyst and the optimal pH reaction conditions for degradation experiments were used to screen the highly reactive titania surface heterojunction system and its optimum application conditions. It provides the possibility of application in the degradation of industrial wastewater and environmental treatment.

Morphology-controlled porous α-Fe2O3/SnO2 nanorods with uniform surface heterostructures and their enhanced acetone gas-sensing properties

Morphology-controlled porous α-Fe2O3/SnO2 nanorods with uniform surface heterostructures have been fabricated by a facile surface modification of rod-like α-Fe2O3 nanomaterials by changing the adding amount of Sn composition, displaying the excellent selectivity and sensitivity of gas-sensing to acetone. The introduction of SnO2 nanoparticles had the great effects on tuning the crystal size, crystallinity, and surface status, as well as the structural stability and phase distribution of α-Fe2O3/SnO2 nanorods. Compared to pure α-Fe2O3, α-Fe2O3/SnO2 heterostructures can exhibit the optimal gas-sensing behavior with the sensitivity up to 53.1 and the response and recovery times decreasing to 9 and 2.5 s at the operating temperature of 260 °C, respectively. The enhanced gas-sensing performance can be mainly attributed to the combination of uniform porous structures, narrow size-distribution, large specific surface area, and heterostructures of the interface between α-Fe2O3 and SnO2.

Inkjet printing of TiO2/AlOOH heterostructures for the formation of interference color images with high optical visibility.

This paper describes a practical approach for the fabrication of highly visible interference color images using sol-gel ink technique and a common desktop inkjet printer. We show the potential of titania-boehmite inks for the production of optical heterostructures on various surfaces, which after drying on air produce optical solid layers with low and high refractive index. The optical properties of the surface heterostructures were adjusted following the principles of antireflection coating resulting in the enhancement of the interference color optical visibility of the prints by as much as 32%. Finally, the presented technique was optimized following the insights into the mechanisms of the drop-surface interactions and the drop-on-surface coalescence to make it suitable for the production of even thickness coatings suitable for printing at a large scale. We propose that the technology described herein is a promising new green and sustainable approach for color printing.

Facile synthesis and enhanced magnetic, photocatalytic properties of one-dimensional Ag@Fe3O4-TiO2

Fe3O4-TiO2 heterostructures were synthesized through co-precipitation method based on TiO2 nanobelts. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibration sample magnetometry (VSM) were used to characterize the heterostructure nanocomposites. The results of XRD proved that the TiO2 nanobelt was anatase which was the most suitable crystal form for photocatalysis. SEM and TEM analysis indicated that Fe3O4 nanoparticles were adhere to TiO2 nanobelts which have one-dimensional structure with 100–200nm in width. The VSM measurements showed that the photocatalyst can be easily recovered by an extemal magnetic field. X-ray photoelectron spectroscopy (XPS) of Ag@Fe3O4-TiO2 nanocomposites studies confirm that Ag is in Ag0 state. Finally, the photodegradation of rhodamine B (RhB) by the obtained magnetic photocatalyst was investigated via UV–vis absorption spectra. The photocatalytic activity of the composites was observed to be lower compared to bare TiO2 due to the higher degree of recombination reactions after combined with Fe3O4 nanoparticles. After coated the composite of 15% Fe3O4-TiO2 with Ag, the new nanocomposite of Ag@Fe3O4-TiO2 can be easily recovered after photocatalysis by an extemal magnetic field and showed enhanced photocatalytic activity. The mechanisms for the exhibited enhanced photocatalytic effect of Ag nanoparticle decorated Fe3O4-TiO2 nanocomposites with surface heterostructures are discussed.

RuO2/TiO2 nanobelt heterostructures with enhanced photocatalytic activity and gas-phase selective oxidation of benzyl alcohol

Based on energy band matching between RuO2 and TiO2, the RuO2/TiO2 nanobelt heterostructures are designed and fabricated. The formed heterostructures can efficiently enhance the separation of photogenerated electron-hole pairs and accelerate the transport of charges. Thanks to above-mentioned advantages, the RuO2/TiO2 nanobelt heterostructures exhibit an improved photocatalytic performance compared with P25, TiO2, and RuO2 under UV and visible light irradiation. Moreover, the nanopapers based on RuO2/TiO2 nanobelt heterostructures have been prepared via a modified paper-making process. The paper-like porous RuO2/TiO2 nanobelt heterostructures are applied in heterogeneous catalysis and present enhanced activity and selectivity for catalyzing aerobic oxidation of benzyl acohol. These results may provide a paradigm to fabricate and design the one-dimensional TiO2 nanostructured surface heterostructures with high efficiency and performance.

ChemInform Abstract: Structure, Synthesis, and Applications of TiO2 Nanobelts

AbstractReview: [189 refs.

Structure, synthesis, and applications of TiO2 nanobelts.

TiO2 semiconductor nanobelts have unique structural and functional properties, which lead to great potential in many fields, including photovoltaics, photocatalysis, energy storage, gas sensors, biosensors, and even biomaterials. A review of synthetic methods, properties, surface modification, and applications of TiO2 nanobelts is presented here. The structural features and basic properties of TiO2 nanobelts are systematically discussed, with the many applications of TiO2 nanobelts in the fields of photocatalysis, solar cells, gas sensors, biosensors, and lithium-ion batteries then introduced. Research efforts that aim to overcome the intrinsic drawbacks of TiO2 nanobelts are also highlighted. These efforts are focused on the rational design and modification of TiO2 nanobelts by doping with heteroatoms and/or forming surface heterostructures, to improve their desirable properties. Subsequently, the various types of surface heterostructures obtained by coupling TiO2 nanobelts with metal and metal oxide nanoparticles, chalcogenides, and conducting polymers are described. Further, the charge separation and electron transfer at the interfaces of these heterostructures are also discussed. These properties are related to improved sensitivity and selectivity for specific gases and biomolecules, as well as enhanced UV and visible light photocatalytic properties. The progress in developments of near-infrared-active photocatalysts based on TiO2 nanobelts is also highlighted. Finally, an outline of important directions of future research into the synthesis, modification, and applications of this unique material is given.

ChemInform Abstract: Recent Progress in Design, Synthesis, and Applications of One‐Dimensional TiO2 Nanostructured Surface Heterostructures

AbstractReview: 50 refs.

Enhanced Photocatalytic Property of Reduced Graphene Oxide/TiO2 Nanobelt Surface Heterostructures Constructed by an In Situ Photochemical Reduction Method

A facile method is proposed to assemble graphene oxide (GO) on the surface of a TiO2 nanobelt followed by an in situ photocatalytic reduction to form reduced graphene oxide (rGO)/TiO2 nanobelt surface heterostructures. The special colloidal properties of GO and TiO2 nanobelt are exploited as well as the photocatalytic properties of TiO2 . Using water-ethanol solvent mixtures, GO nanosheets are tightly wrapped around the surface of the TiO2 nanobelts through an aggregation process and are then reduced in situ under UV-light irradiation to form rGO/TiO2 nanobelt surface heterostructures. The heterostructures enhance the separation of the photoinduced carriers, which results in a higher photocurrent due to the special electronic characteristics of rGO. Compared to TiO2 nanobelts, the rGO/TiO2 nanobelt surface heterostructures possess higher photocatalytic activity for the degradation of methyl orange and for the production of hydrogen from water, as well as excellent recyclability, with no loss of activity over five cycles.