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Solar-driven interfacial evaporation has shown great promise for desalination due to its high photothermal conversion efficiency. However, for interfacial evaporation, the evaporator must have superior mechanical quality and strong thermal stability. To this end, ceramic nanofibrous mats with good mechanical strength can serve as a stable substrate for desalination. Herein, with the aid of finite element analysis, flexible Al2O3/TiO2 nanofibrous mats with robust mechanical properties are fabricated, where the stress dispersion greatly facilitates the Al2O3/TiO2 nanospheres to be uniformly dispersed into the mat. The flexible nanofibrous mats exhibit a high tensile strength up to 2.18 MPa. Afterward, a two-dimensional (2D) Al2O3/TiO2/MXene mat is constructed by a simple drop-casting method. Interestingly, the evaporation rate of the Al2O3/TiO2/MXene-2 mat reached 1.43 kg m−2 h−1, and the light-to-vapor energy conversion efficiency can reach 102% at a power density of 1.0 kW m−2. To measure the desalination efficiency, five ion concentrations in the collected water were found to be well below the safe salinity levels defined by standards set by the World Health Organization and U.S Environmental Protection Agency. Utilizing basic origami technology, the three-dimensional (3D) photothermal evaporator was integrated with the 2D mat due to its flexibility and ductility. Additionally, the evaporation rate increased to 1.61 kg m−2 h−1. This study is critical in the design of composite ceramic nanofiber materials with high flexibility and photothermal conversion efficiency for multifunctional desalination. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) nanomaterials are critical to producing clean oxygenation or value-added chemical production by utilizing sustainable solar energy, but are always limited by simultaneous integration of architectural engineering and electronic regulation in one structure. Directed by density functional theory (DFT) calculations and finite element analysis (FEA), the bio-inspired ivy-like Fe2O3 heterostructures with enriched oxygen defects on TiO2 nanofibers are designed for boosting PEC performances. Ivy-like Fe2O3 photo-sheets remarkably enhanced the light harvesting by multiple light-mater interactions. The oxygen vacancies on Fe2O3 photo-sheets could aid the photons catching and promote the reactivity at active sites. More importantly, demonstrated by a well-designed dynamic observation, the abundant tip-edges within ivy-like Fe2O3 photo-sheets enabled the surface of heterostructure with hydrophilic and aerophobic properties. The functionalized surface allowed the rapid desorption of produced bubbles and thus ensured a high density of unoccupied active sites for electrolyte accessing. Featured by these attributes, the Fe2O3@TiO2 nanofibers delivered an excellent photocurrent of 40.8 mA/mg, high donor density (1.2 × 1018 cm−3), and rapid oxygen production rate (1 mmol/(L·h)). This work demonstrates a new strategy on nano-structural design for enhancing light-harvesting and making a hydrophilic/aerophobic surface on low-dimensional oxide nanomaterial, holding great potential on designing high-performance PEC devices for producing survival source gas, carbon-neutral fuel, and valued-chemicals. [ABSTRACT FROM AUTHOR]

Up to now, the synthesis of non‐ligand‐capped 2D transition‐metal nanostructures remained big synthetic challenges. Herein, ultrathin and microporous AlOOH/Al2O3 nanosheets were topologically grown on the surface of TiO2‐based nanofibers by a water‐only hydrothermal strategy starting from electrospun Al2O3/TiO2 nanofibers. The TiO2 nanofibers lowered the surface energy for the sustained‐released aluminum species and thereby allowed them in situ hydrated to laminar AlOOH. The metastable AlOOH tended to dehydrate to Al2O3 simultaneously, leaving a well‐maintained 2D structure with sharp corners and steps, as well as enriched micropores. The nanosheets‐on‐nanofibers exhibited 2856–3370 mg/g of adsorption capacity toward RhB and an efficient removal efficiency over 70% at high throughput (30 mL/h). The promoted light‐harvesting by the perpendicularly attached nanosheets further endowed a significant photodegradation for RhB within 1 h. The presented green and facile approach toward the fabrication of 2D metal oxide nanostructures paves the way to a new variety of oxide nanomaterials. [ABSTRACT FROM AUTHOR]

The thermal stability of CeO2 nanomaterials can directly impact both the uniformity of the supported catalysts and the catalytic behavior of CeO2 itself. However, knowledge about the thermal stability of CeO2 is still deficient. Here, we conduct in-situ transmission electron microscopy experiments and theoretical calculations to elucidate the thermal stability of CeO2 nanomaterials under different environments. A sinter (< 700 °C) and a structural decomposition (> 700 °C) are observed within CeO2 nanoflowers under O2. The sinter firstly occurs among the nanoflowers' monomers and then the sintered nanoparticles structurally decompose to tiny nanoparticles from the strain interface. Under a vacuum environment, the CeO2 nanoflowers firstly undergo a transition from cubic fluorite CeO2 to hexagonal Ce2O3, accompanied by the oxygen release. The Ce2O3 nanoparticles further atomically sublimate from the edges to the center under high temperatures. Theoretical calculation results reveal a considerably lower energy barrier for the structural decomposition under O2 and for the sublimation under vacuum. This work provides a perspective on the structural design and performance optimization of CeO2-based catalysts. [ABSTRACT FROM AUTHOR]

Solar-driven evaporation is highly promising for sustainable freshwater production without high energy-consumption. Till now, it has still been challenging to achieve both high performance and cost-effectiveness within one evaporator. In addition, the rarely reported strategy overcomes the obstacles of emerging microplastic-pollution in water sources and poor all-day-round evaporation. Herein, a low-cost, high-efficiency, biomass-derived three-dimensional (3D) graphene/cotton sponge with gradient vertical microchannels was readily constructed by simply stretching cotton. It served as a versatile photothermal platform with a high evaporation rate (2.49 kg m−2 h−1, normalized to both the top and side surfaces) and could withstand a large external stress of up to 8750-times its weight. Moreover, in the first attempt to efficiently evaporate water (90.6%) from a microplastic-polluted source, nearly 100% of the polyethylene (PE) microfibers were removed from evaporated water by 3D MoS2/graphene/cotton via reactive oxygen species attack and multi-level interception. New in situ FTIR microscopy technology was employed to accurately monitor the degradation mechanism of the PE microplastics. The PE degradation efficiency was as high as 19% in oxygen-enriched water, predominantly contributed by reactive O2˙−, and could be easily enhanced to 32% with the aid of additional reactive species (e.g., ˙HOO and H2O2) in 1 h. Besides, under the guidance of finite element analysis (FEA), a phase-change polyethylene glycol (PEG) layer was functionalized outside the graphene/cotton. Notably, it possessed a remarkably high all-day-round evaporation rate (1.63 kg per m2 per h per day, 1.42-times that achieved by a traditional evaporator without phase-change function) by utilizing thermal energy in the dark. This work gives promising alternative strategies for low-cost clean-water harvesting from microplastic-pollution and sustainable evaporation even under dark conditions. [ABSTRACT FROM AUTHOR]

As solar energy is readily available in most climates, solar evaporation plays a critical role in freshwater production and can be further integrated into various important applications. Demonstrated here is a plasmonic-antenna-coupled aerogel with confined heat at the micro and nanoscale levels based on vertically aligned Au/N-doped reduced graphene oxide (N-RGO) meshes towards an effective solar evaporation. The gradient microchannels in the aerogel were ably constructed by introducing gradient anti-freeze (i.e., NH4OH) concentrations in the hydrogel before freeze-drying to concentrate water to a central region (i.e., the hot zone). As plasmonic nanoantennas, Au nanoparticles were integrated on N-RGO meshes in/around nanopores to enhance energy harvesting and accurately localize heat for promoted in situ evaporation. Featuring broadband absorption (99.7%) and plasmon-enhanced photothermal conversion, this aerogel exhibits superior solar-to-vapor conversion (97.1%) and a high evaporation rate (2.72 kg m−2 h−1, normalized to both top and side surfaces), along with salt-resistance. Besides, the aerogel has been demonstrated as a novel solar-driven, anti-gravity catalytic reactor toward high value-added chemical (e.g., 4-aminophenol) conversions with high efficiency by localizing heat on reaction sites. This work provides an attractive strategy for the elegant manipulation of water and energy at multi-levels in solar evaporation and shows a novel approach to anti-gravity catalytic conversions driven by sunlight. [ABSTRACT FROM AUTHOR]

Structural optimization and surface engineering of photocatalysts are considered as promising approaches to improve their performances effectively. The precise control of morphology and compositions during synthesis of photocatalysts is important but yet challenging. In this work, without any aid of surfactant, urchin-like reduced graphene oxide/sodium titanate (RGO/Na2Ti3O7) microspheres were fabricated by a facile, one-pot hydrothermal reaction with good reproducibility. Both microsized and nanosized graphene oxide sheets can serve as catalysts of manipulating the growth kinetics of urchin-like Na2Ti3O7 microspheres by accelerating nucleation while inhibiting Ostwald ripening. The coupling of hierarchical Na2Ti3O7 with RGO significantly enhanced photoelectrochemical and photocatalytic performances under visible-light irradiation. The steady-state photocurrent density of RGO/Na2Ti3O7-based photoanode was 13.6 times higher than those based on pristine Na2Ti3O7, thanks to the narrowed bandgap, enhanced light harvesting, and effective electron transfer. The surfactant-free RGO/Na2Ti3O7 microspheres were further demonstrated as photocatalysts endowed with photothermal effect enhanced photocatalytic activity. Toward H2 generation by hydrolysis of ammonia borane, the maximum hydrogen production rate of RGO/Na2Ti3O7 reached 2.73 times higher than that of Na2Ti3O7, mainly due to the excellent photothermal efficiency up to 67.2% (higher than that of noble metal, e.g., Au dumbbell-like structure). It is believed that our understanding and reliable strategy could be extendable to construct new photocatalysts and systems toward effective solar energy harvesting and utilizations. [ABSTRACT FROM AUTHOR]

In this work, shape manipulation in porous CeO2 nanofibers was successfully achieved by a simple electrospinning technology with high quality and high reproducibility. By simply tuning the electric field strength during electrospinning, the diameter of as-spun nanofibers composed of Ce(acac)3 and polyvinylpyrrolidone can be precisely controlled. As a result, the morphology of nanofibers can change from columnar to celery-like and belt-like structure. The formation mechanism of this intriguing diameter-dependent morphology can be assigned to the gradient evaporation of solvent across the nanofiber. After calcination at 500 °C, porous CeO2 nanofibers were obtained, showing unusually observed celery-like or belt-like morphologies. These intriguing CeO2 nanofibers exhibited good thermal stability in terms of phase structures and morphologies up to 700 °C. The fibrous CeO2 mats were active toward soot combustion with decreased activation energy, compared with commercial samples. Among three kinds of shapes, the fibrous CeO2 mats made of columnar-like nanofibers were endowed with the lowest activation energy of 120.1 kJ/mol, due to the most effective contact between soot and CeO2 surface, regardless a loose contact mode. [ABSTRACT FROM AUTHOR]

Catalyst sintering, a main cause of the loss of catalytic activity and/or selectivity at high reaction temperatures, is a major concern and grand challenge in the general area of heterogeneous catalysis. Although all heterogeneous catalysts are inevitably subjected to sintering during their operation, the immediate and drastic consequences can be mitigated by carefully engineering the catalytic particles and their interactions with the supports. In this tutorial review, we highlight recent progress in understanding the physical chemistry and materials science involved in sintering, including the discussion of advanced techniques, such as in situ microscopy and spectroscopy, for investigating the sintering process and its rate. We also discuss strategies for the design and rational fabrication of sinter-resistant catalysts. Finally, we showcase recent success in improving the thermal stability and thus sinter resistance of supported catalytic systems. [ABSTRACT FROM AUTHOR]

Abstract: New N‐doped reduced graphene oxide (N‐RGO) meshes are facile fabricated by selective etching of 3–5 nm nanopores, with controllable doping of N dopants at an ultrahigh N/C ratio up to 15.6 at%, from pristine graphene oxide sheets in one‐pot hydrothermal reaction. The N‐RGO meshes are illustrated to be an efficient metal‐free catalyst toward hydrogenation of 4‐nitrophenol, with new catalytic behaviors emerging in following three aspects: (i) tunable kinetics following pseudofirst order from commonly observed pseudozero order; (ii) strikingly improved activity with 26‐fold increased rate constant (1.0 s−1 g−1 L); (iii) no induction time required prior to reaction due to depressed back conversion, and dramatically decreased apparent activation energy (Ea) (17 kJ mol−1). The origin of these new catalytic properties can be assigned to the synergetic effects between graphitic N doping and structural defects arising from nanopores. Deeper understanding unveils that the concentration of graphitic N is inverse proportion to Ea, while the pyrrolic N has no impact on this reaction, and oxygenate groups hampers it. The porous nature allows the N‐RGO meshes to conduct catalyze reactions in continuous flow fashion. [ABSTRACT FROM AUTHOR]

Precious metals are widely used as catalysts in industry. It is of critical importance to keep the precious metal ions leached from catalysts at a level below one part per million (ppm) in the final products and to recycle the expensive precious metals. Here we demonstrate a simple and effective method for scavenging precious metal ions from an aqueous solution and thereby reduce their concentrations down to the parts per billion (ppb) level. The key component is a filtration membrane comprised of titania (TiO2) nanofibers whose surface has been functionalized with a silane bearing amino or thiol group. When operated under continuous flow at a rate of 1 mLmin-1 and at room temperature, up to 99.95% of the Pd2+ ions could be removed from a stock solution with an initial concentration of 100 ppm. This work offers a viable strategy not only for the removal of precious metal ions but also for recovering and further recycling them for use as catalysts. For example, the captured Pd2+ ions could be converted to nanoparticles and used as catalysts for organic reactions such as Suzuki coupling in a continuous flow reactor. This system can be potentially applied to pharmaceutical industry and waste stream treatment. [ABSTRACT FROM AUTHOR]

Supported metal catalysts are critical to many important chemical reactions, but the weak metal/support interaction is an obstacle to the success of remarkable catalytic performance. This paper reports rational-designed novel Pt supports, consisting of reduced graphene oxide sheets decorated with both Fe2O3 nanorods and N-dopants (denoted as Fe2O3/N-RGO), for Pt photodeposition driven by visible light in a controllable fashion. The 2-3 nm Pt nanocrystals primarily nucleated on rough Fe2O3 nanorods, and interacted strongly with special sites on the Fe2O3 surface using unsaturated vacant orbitals. At the same time, the accelerated photodegradation of undesirable PVP allowed the Pt nanocrystals with clean active sites. The supported Pt showed impressive activity and had a 7-times higher reaction rate constant (11.4 s-1 mg-1) towards 4-nitrophenol reduction, compared with that of free Pt, due to the synergetic effect within the whole Pt/Fe2O3/N-RGO catalysts and the doping of N atoms which acted as new metal-free catalytic centers in N-RGO sheets. We further demonstrated that the ternary catalyst could be easily removed through magnetic separation from the system. This new strategy is extendible to other heterogeneous catalysts with different components. [ABSTRACT FROM AUTHOR]

This paper reports a facile fabrication of N-doped graphene quantum dots (N-GQDs) showing controllable chemical properties through a hydrothermal treatment. The N-GQDs have a uniform size of 3.06 ± 0.78 nm and prefer the equilibrium shapes of circle and ellipse due to the minimization of edge free energy. The N/ C atomic ratio in N-GQDs can be precisely tailored in a range from 8.3 at% to 15.8 at% by simply controlling the concentration of N source (ammonium hydroxide). One order of magnitude quantum yield of 34.5% is achieved by N-GQDs, compared with the N-free GQDs, as the substitutional N has an essential role in more effective radiative emission. Excessive N dopants in N-GQDs can lead to photoluminescence quenching, through nonradiative transition back to the ground state. The N-GQDs are further found to be suitable as photocurrent conversion materials due to benign energy matching with anatase nanofibers, the ultrafast electron injection at their interface, and efficient electron transfer. This work provides an efficient and inspiring approach to engineering both chemical components and physical properties of N-GQDs, and will therefore promote their basic research and applications in energy conversion. [ABSTRACT FROM AUTHOR]

For TiO2-based photoanodes, the interfacial coupling between TiO2 and conductive materials (e.g., carbon) plays a vital role in determining the electron transfer efficiency and thus photoelectrical performance. In this paper, we describe a facile approach to effectively engineering the interfacial coupling between reduced graphene oxide (RGO) and TiO2 in well-designed one-dimensional (1D) RGO-wrapped TiO2 nanofibers, which act as ultrafast electron transfer bridges when implanted in photoanodes. The 3–5 nm RGO nanoshells were hybridized with TiO2 nanofibers as an electron donor component via d–π electron orbital overlap between C and Ti atoms, by adopting a thermal reduction at 450 °C. Remarkable photoelectric improvement, in terms of high photocurrent density by 2.2-fold and ultralow charge transfer resistance (Rct) by 0.2-fold, is ascribed to the interfacial charge transfer. Completely reduced RGO in RGO/TiO2 nanofibers was not necessary at the expense of their hydrophilicity, as it led to unexpected isolation in the photoanodes. The thermal reduction temperature of RGO/TiO2 nanofibers was found to be critical, and a maximal photocurrent density could be achieved by 2.7-fold at 530 °C. An excess of RGO/TiO2 nanofibers of more than 5 wt% had a degrading effect on the photoelectrical activity, largely due to the light-block effect and isolation in the matrix. This strategy provides new insight for tuning the intrinsic chemical and/or physical properties of well-designed semiconductor nanostructures with promising photoactivities in highly efficient photovoltaic devices. [ABSTRACT FROM AUTHOR]

We report the synthesis of a novel compound, 9,9-bis(3′-aminopropyl)-2,7-diphenylfluorene (BAPDPF), and a new approach to graft the BAPDPF onto a CdS quantum dot (QD) surface via an acylation reaction. FT-IR and TGA characterizations indicate the formation of robust bonding between BAPDPF and QDs; the structures of the bare QDs and BAPDPF–CdS QD hybrid nanocomposites estimated by transmission electron microscopy (TEM) showed that they have the same size of about 3.5 nm. The extent of the spectral overlap between the emission of BAPDPF and absorption of QDs, and the change of fluorescence emission for the organic and inorganic components of the hybrid, demonstrate that the energy transfer process occurs from BAPDPF to the CdS QDs. The energy transfer of about 44% efficiency is corroborated by time-resolved fluorescence measurements, and then the solid-state photoluminescence quantum yield (PLQY) of the nanocomposite is measured using an integrating sphere and a conventional fluorimeter. Because of the fact that the PLQY of the nanocomposite is 9.1 times larger than that of the pristine QDs, due to the energy transfer between the donor and the acceptor and passivation effects on the surface of the acceptor, the presented BAPDPF–CdS QD hybrid nanocomposites are potentially interesting in nanoparticle-based light-emitting devices. [ABSTRACT FROM AUTHOR]

Based on the solid-state electrochemiluminescence (ECL) of an electrogenerated polypyrrole tagged with tris(2,2′-bipyridyl)ruthenium(II) complex ( denoted as polypyr-Ru), a new ethanol biosensor was fabricated by casting the composite of alcohol dehydrogenase (ADH) and laponite colloids onto the polypyr-Ru /Pt electrode. The two layer structure keeps the good robustness of the biosensor due to the electrostatic interaction between the negatively charged biocomposite coating and the positively charged polypyr-Ru. The morphology of the laponite-ADH composite coating is characterized by scanning electron microscopy. The electrochemical and ECL properties of the modified electrodes are investigated by cyclic voltammetry. The parameters concerning the ECL biosensor such as the amount of enzyme usage, the appropriate pH are optimized. The resulted ECL biosensor shows a good performance to detect ethanol. [ABSTRACT FROM AUTHOR]