Significantly enhanced the light absorption and charge separation of Bi0.5Na0.5TiO3 by coupling with CdS for high-performance piezo-photocatalysis.

Sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT) is a typical lead-free piezoelectric material with perovskite structure, which exhibits great potential as piezo-photocatalyst but limited by the little response on visible light and insufficient carriers for efficient catalytic reactions. Herein, a novel BNT/CdS heterojunction was facilely synthesized by the two-step hydrothermal process for significantly enhanced piezo-photocatalytic degradation of organic dyes. The CdS nanoparticles with 35 nm in diameter are uniformly decorated on the highly crystallized BNT spheres. The obtained BNT/CdS heterojunction displays strong absorption of visible light because of the narrow band gap of CdS. Due to the strong built-in electric field under ultrasonic and efficient excitation by visible light, the photogenerated carriers can be efficiently separated at the BNT/CdS interface and migrate to the surface for catalytic reactions. As a result, the BNT/CdS shows much higher piezo-photocatalytic activity than that of BNT and can degrade 99% RhB within 60 min. Meanwhile, the piezo-photocatalytic performance of BNT/CdS is far better than that of individual photocatalysis or piezocatalysis. Moreover, the catalytic experiments in the presence of different scavengers indicate that ·O2- is the predominant active specie. The synthetic process is simple, low-cost, and controllable to produce high-performance BNT/CdS and is believed to show promising application prospect.

Unexpected optical limiting properties from MoS2 nanosheets modified by a semiconductive polymer.

Direct solvent exfoliation of bulk MoS2 with the assistance of poly(3-hexylthiophene) (P3HT) produces a novel two-dimensional organic/inorganic semiconductor hetero-junction. The obtained P3HT-MoS2 nanohybrid exhibits unexpected optical limiting properties in contrast to the saturated absorption behavior of both P3HT and MoS2, showing potential in future photoelectric applications.

Broadband optical limiting response of a graphene-PbS nanohybrid.

Graphene-based materials have shown promising nonlinear optical properties in the visible range. To extend their nonlinear optical response to the near infrared (NIR) region, we prepared a new nanohybrid consisting of uniform PbS quantum dots (QDs) attached on the reduced graphene oxide, named rGO-PbS, via a facile, low-cost, and phosphine-free method. The rGO-PbS nanohybrid exhibited superior optical limiting properties to either graphene oxide or PbS QDs upon both 532 nm and 1064 nm excitation in the nanosecond laser pulse regime, which is attributed to the synergetic effects stemming from charge transfer between the two components. Meanwhile, the thin films containing the rGO-PbS nanohybrid dispersed in polymethylmethacrylate (PMMA) also showed excellent optical limiting properties with high transparency, implying the potential applications of this hybrid material in broadband nonlinear optical devices.

Size-dependent nonlinear optical properties of atomically thin transition metal dichalcogenide nanosheets.

Size-dependent nonlinear optical properties of modification-free transition metal dichalcogenide (TMD) nanosheets are reported, including MoS2 , WS2 , and NbSe2 . Firstly, a gradient centrifugation method is demonstrated to separate the TMD nanosheets into different sizes. The successful size separation allows the study of size-dependent nonlinear optical properties of nanoscale TMD materials for the first time. Z-scan measurements indicate that the dispersion of MoS2 and WS2 nanosheets that are 50-60 nm thick leads to reverse saturable absorption (RSA), which is in contrast to the saturable absorption (SA) seen in the thicker samples. Moreover, the NbSe2 nanosheets show no size-dependent effects because of their metallic nature. The mechanism behind the size-dependent nonlinear optical properties of the semiconductive TMD nanosheets is revealed by transient transmission spectra measurements.

Fabrication of microlens arrays by localized hydrolysis in water droplet microreactors.

We report a facile self-assembly strategy for fabricating TiO2 microlens arrays by localized hydrolysis of TiCl4 precursor in water droplets. Microcontact printing was used to define hydrophilic areas on a substrate for space resolved hydrolytic reaction. The water droplets served as the templates, reactant, and microreactors. Highly ordered TiO2 microlens arrays could be produced, which exhibit excellent ability to focus light. Because both size and shape of the final TiO2 microlens can be controlled by the printed chemical pattern and the precursor concentration, it is possible to define TiO2 microlens arrays with different imaging properties. This new method shows attractive features of simplicity, low cost, and requires no heating process, hence is suitable for a range of applications.

Monitoring the layer-by-layer self-assembly of graphene and graphene oxide by spectroscopic ellipsometry.

Thin films of graphene oxide, graphene and copper (II) phthalocyanine dye have been successfully fabricated by electrostatic layer-by-layer (LbL) assembly approach. We present the first variable angle spectroscopic ellipsometry (VASE) investigation on these graphene-dye hybrid thin films. The thickness evaluation suggested that our LbL assembly process produces highly uniform and reproducible thin films. We demonstrate that the refractive indices of the graphene-dye thin films undergo dramatic variation in the range close to the absorption of the dyes. This investigation provides new insight to the optical properties of graphene containing thin films and shall help to establish an appropriate optical model for graphene-based hybrid materials.

High spatial resolution label-free detection of antigen-antibody binding on patterned surface by imaging ellipsometry.

High spatial resolution and large area thickness mapping of label-free protein microarray has been achieved using imaging ellipsometry (IE) under optimized conditions. The protein patterns with feature size down to 8×8 µm(2) was readily imaged, and the binding between the surface immobilized antigen and the antibody was monitored. Quantitative thickness analysis of antibody-antigen binding on the 32×32 µm(2) micron spots was successfully performed, and we have obtained a limit of detection as low as 1.2 pg/spot. This work demonstrates that appropriately optimized IE could be used as a highly sensitive and high through-put label-free technique for studying surface antigen-antibody recognition in sub-40 µm scale.