Rapid High-Contrast Photoreversible Coloration of Surface-Functionalized N-Doped TiO2 Nanocrystals for Rewritable Light-Printing.

Pristine titanium dioxide (TiO2 ) changes color from white to black when it is reduced from TiIV to TiIII by photoexcited electrons. However, the black coloration requires substantial light energy to create, and it vanishes instantaneously upon exposure to air. This work reports the synthesis of surface-functionalized N-doped TiO2 nanocrystals that rapidly change color (i.e., within seconds) from whitish to black under low-power irradiation with excellent color stability in atmospheric conditions. The N-doping plays a critical role in promoting the surface-adsorption of polyol groups to stabilize the TiIII species and accelerate the coloration process. A rewritable paper fabricated using these nanocrystals exhibits excellent writing and erasing reversibility in response to UV irradiation and oxygen exposure. The low-cost, rapid response, excellent reversibility, and good color stability are vital advantages of N-doped TiO2 nanocrystals for color-switching applications.

Creation and Reconstruction of Thermochromic Au Nanorods with Surface Concavity.

Conventional colloidal syntheses typically produce nanostructures with positive curvatures due to thermodynamic preference. Here, we demonstrate the creation of surface concavity in Au nanorods through seed-mediated growth in confined spaces and report their thermochromic responses to temperature changes. The unique surface concavity is created by templating against Fe3O4 nanorods, producing a new concavity-sensitive plasmonic band. Due to the high surface energy, the metastable nanorods can be reconstructed at a moderate temperature, enabling convenient and precise tuning of their plasmonic properties by aging in different solvents. Such structural reconstruction of concave Au nanorods enables the fabrication of thermochromic plasmonic films that can display images with vivid color changes or exhibit encrypted, invisible information upon aging. This templating strategy is universal in creating concave nanostructures, which may open the door to designing new nanostructures with promising applications in sensing, anticounterfeiting, information encryption, and displays.

Integrated Evaporator for Efficient Solar-Driven Interfacial Steam Generation.

Solar-driven interfacial steam generation is a promising technique for clean water production because it can minimize thermal loss by localizing solar-to-heat conversion at the air/liquid interface. Here we report an integrated solar evaporator by partially growing 2D polypyrrole microsheets within a melamine foam through chemical vapor polymerization. These microsheets can induce multiple light reflections within the foam, enable omnidirectional light absorption, provide abundant surfaces to promote heat transfer, and achieve spatially defined hydrophobicity to facilitate vapor escape. Meanwhile, the inherent hydrophilicity of the bottom part of the foam promotes spontaneous upward water transport and suppresses heat loss. The composite foam exhibits an excellent apparent evaporation rate of ∼2 kg/(m2·h) and solar-to-vapor efficiency of ∼91%. The combined advantages of large surface area, high efficiency, low cost, all-weather application, excellent durability, and scalable manufacturing make our integrated design promising for fabricating large-scale solar steam generation systems that are suitable for practical clean water production.

Dynamic Color-Switching of Plasmonic Nanoparticle Films.

The fast and reversible switching of plasmonic color holds great promise for many applications, while its realization has been mainly limited to solution phases, achieving solid-state plasmonic color-switching has remained a significant challenge owing to the lack of strategies in dynamically controlling the nanoparticle separation and their plasmonic coupling. Herein, we report a novel strategy to fabricate plasmonic color-switchable silver nanoparticle (AgNP) films. Using poly(acrylic acid) (PAA) as the capping ligand and sodium borate as the salt, the borate hydrolyzes rapidly in response to moisture and produces OH- ions, which subsequently deprotonate the PAA on AgNPs, change the surface charge, and enable reversible tuning of the plasmonic coupling among adjacent AgNPs to exhibit plasmonic color-switching. Such plasmonic films can be printed as high-resolution invisible patterns, which can be readily revealed with high contrast by exposure to trace amounts of water vapor.

Space-Confined Seeded Growth of Cu Nanorods with Strong Surface Plasmon Resonance for Photothermal Actuation.

Herein, we show that copper nanostructures, if made anisotropic, can exhibit strong surface plasmon resonance comparable to that of gold and silver counterparts in the near-infrared spectrum. Further, we demonstrate that a robust confined seeded growth strategy allows the production of high-quality samples with excellent control over their size, morphology, and plasmon resonance frequency. As an example, copper nanorods (CuNRs) are successfully grown in a limited space of preformed rod-shaped polymer nanocapsules, thereby avoiding the complex nucleation kinetics involved in the conventional synthesis. The method is unique in that it enables the flexible control and fine-tuning of the aspect ratio and the plasmonic resonance. We also show the high efficiency and stability of the as-synthesized CuNRs in photothermal conversion and demonstrate their incorporation into nanocomposite polymer films that can be used as active components for constructing light-responsive actuators and microrobots.

Corrosion Inhibition of Carbon Steel in a Sour (H2S) Environment by an Acryloyl-Based Polymer.

Corrosion poses safety and operational challenges in the oil and gas field, particularly in a sour environment. Corrosion inhibitors (CIs) are thus employed to protect the integrity of industrial assets. However, CIs have the potential to dramatically impair the effectiveness of other co-additives, such as kinetic hydrate inhibitors (KHIs). Here, we propose an acryloyl-based copolymer, previously used as a KHI, as an effective CI. The copolymer formulation provided a corrosion inhibition efficiency of up to 90% in a gas production environment, implying that it can reduce or even eliminate the need for an additional dedicated CI in the system. It also demonstrated a corrosion inhibition efficiency of up to 60% under field-simulated conditions for a wet sour crude processing environment. Molecular modeling suggests that the enhanced corrosion protection is imparted by the favorable interaction of the heteroatoms of the copolymer with the steel surface, potentially displacing adhered water molecules. All in all, we show that an acryloyl-based copolymer with dual functionalities can potentially overcome issues caused by incompatibilities in a sour environment, resulting in significant cost savings and operational ease.

MoS2/FeS Nanocomposite Catalyst for Efficient Fenton Reaction.

Nanocomposites containing FeS as catalyst and MoS2 as cocatalyst have been synthesized toward efficient heterogeneous Fenton reaction. The deposition of FeS nanoparticles in situ on the surface of MoS2 nanosheets creates strong contact between the two components and generates a large number of exposed Mo6+ sites and sulfur vacancies, which contribute to the enhanced degradation rate by accelerating Fe3+/Fe2+ cycling and ensuring rapid electron transfer. In addition, the MoS2/FeS nanocomposite catalysts exhibit the best performance at near-neutral conditions (pH 6.5), which solves the challenges in conventional Fenton reactions such as leaching of metal ions, the formation of iron slurry, and the need of adjusting solution pH. Further, the nanocomposite can maintain high efficiency after many recycling experiments. It is believed that the MoS2/FeS nanocomposite represents an efficient heterogeneous Fenton catalyst that can greatly promote the performance of advanced oxidation processes (AOPs) for solving practical environmental issues.

Metallic Active Sites on MoO2(110) Surface to Catalyze Advanced Oxidation Processes for Efficient Pollutant Removal.

Advanced oxidation processes (AOPs) based on sulfate radicals (SO4⋅-) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO2 as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO4⋅--based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO2, whereas the exposed active sites of Mo(IV) on MoO2 surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO2 as a cocatalyst is a promising technique for large-scale practical environmental remediation.

One-step preparation of reduced graphene oxide aerogel loaded with mesoporous copper ferrite nanocubes: A highly efficient catalyst in microwave-assisted Fenton reaction.

Heterogeneous Fenton reaction is an attractive method for degradation of organic pollutants due to its high efficiency and non-selectivity and it also causes no secondary pollution. However, low degradation rate and poor recyclability of the catalysts limit its applications for water purification. To overcome this, herein, copper ferrite/reduced graphene oxide (CF/rGO) aerogel was prepared by a one-step hydrothermal method, as a highly efficient catalyst for the microwave-assisted Fenton reaction (MAFR). Under optimal conditions (500 W of microwave power, 600 µL of H2O2, 15 mg of catalyst, and 30 mg/L of RhB), the degradation efficiency of CF/rGO aerogel at 1.0 min (95.7%) was higher than that of reference samples at 3.0 min. Thermodynamical study showed the activation energy, enthalpy change, entropy change, and Gibbs free energy change were 0.73 kJ/mol, -49.5 kJ/mol, -0.135 kJ/mol·K, and -6.8 kJ/mol, respectively, indicating that MAFR was an endothermic and non-spontaneous process.Radical trapping experiments showed that OH, O2-, and h+ played a combined role in RhB degradation. Besides high catalytic activity, CF/rGO aerogel also displayed good reusability, showing removal efficiency of 87.4% after 5 cycles. The high efficiency, good reusability, and simple process make CF/rGO aerogel a promising catalyst for wastewater treatment.

Surface-bound sacrificial electron donors in promoting photocatalytic reduction on titania nanocrystals.

Titania nanocrystals have been investigated for fast color switching through photocatalytic reduction of dyes and hexacyanometalate pigments. Here we reveal that direct binding of sacrificial electron donors (SEDs) to the surface of titania nanocrystals can significantly promote the charge transfer rate by more efficiently scavenging photogenerated holes and releasing more photogenerated electrons for reduction reactions. Using diethylene glycol (DEG) as an example, we show that its binding to the nanoparticle surface, which can be achieved either during or after the nanoparticle formation, greatly enhances the photocatalytic reduction in comparison with the case where free DEG molecules are simply added as external SEDs.

An in-situ electropolymerization based sensor for measuring salt content in crude oil.

Determining salt content is a vital procedure in the petroleum industry during the process of crude oil transportation, refining and production. Monitoring the salinity value using a fast and direct technique can substantially lower the cost of crude oil in its processing and its production stages. In the present work, a novel analytical method was developed to detect the amount of salt present in crude oil in a quick and reliable manner. The measurement is based on the rate of in-situ electropolymerization of a monomer such as aniline in association with the salt content in the crude oil. The salt dispersed in the hydrocarbon matrix is used as an electrolyte in the electrolytic system to induce an electropolymerization reaction upon the induction of voltages, in which the salt content is measured corresponding to the polymeric film formation on the working electrode surface. Acetonitrile and N-methylpyrrolidone (NMP) were used in the electrochemical cell as solvents, and cyclic voltammetry tests were performed for Arabian crude oil solutions in the presence of aniline. The method has shown an excellent detection response for very low concentrations of salt. Four Arabian crude oils with salt concentrations of 34.2, 28.5, 14.3 and 5.71 mg L(-1) have produced current intensity of 180.1, 172.6, 148.1 and 134.2 µA at an applied current potential of 1.75 V (vs. Ag/AgCl), respectively. A Calibration curve was obtained in the range of 5-35 mg L(-1), giving limits of detection and quantitation at 1.98 and 5.95 mg L(-1), respectively. The in-situ electropolymerization based sensor has significant advantages over the existing techniques of salt monitoring in crude oil such as fast response, temperature independency, electrode stability, and minimum sample preparation.