Single-layer graphene prevents Cassie-wetting failure of structured hydrophobic surface for efficient condensation

"Floating Catalytic Foam" with prominent heat-induced convection for the effective photocatalytic removal of antibiotics

Immobilized photocatalysts represent a promising candidate for the wastewater treatments due to their good reusability, high stability and low eco-risk. Mass transfer within the immobilized catalytic bed is a crucial process that determines the contacting, adsorption, and degradation kinetics in the photodegradation. In this study, a floating catalytic foam (FCF) with a prominent pumping effect was designed to promote mass transfer. The polyurethane foam immobilized with rGO/TiO2/ultrathin-g-C3N4 photocatalyst (PRTCN) was prepared by a simple dip-coating and Uv-light aging process. It was found that the hydrophilic-hydrophobic interfaces could not only contribute to the floating of the catalyst but also establish a temperature gradient across the floating immobilized catalyst. In addition, the temperature gradient induced convection could serve as a built-in pump to effectively promote the diffusion and adsorption of target antibiotic molecules during the photocatalytic process. Therefore, the PRTCN demonstrated a high photodegradation and mineralization efficiency with excellent reusability and anti-interference capability. Moreover, the photodegradation mechanism and the intermediates' toxicity of norfloxacin were detailly investigated by ultra-high resolution electrospray time-of-flight mass spectrometry, density functional theory simulation and ECOSAR estimation. This work proposed a facile and sustainable strategy to enhance the mass transfer problem on immobilized photocatalysts, which could promote the application of the immobilized photocatalysts in the real water-treatment scenarios.

Discontinuous dewetting dynamics of highly viscous droplets on chemically heterogeneous substrates

HYPOTHESIS

Droplet spreading on heterogeneous (chemical/structural) surfaces has revealed local disturbances that affect the advancing contact line. With droplet dewetting being less studied, we hypothesize that a receding droplet can be perturbed by localized heterogeneity which leads to irregular and discontinuous dewetting of the substrate.

EXPERIMENTS

The sessile drop method was used to study droplet dewetting at a wettability boundary. One-half of a hydrophilic surface was hydrophobically modified with either i) methyloctyldichlorosilane or ii) clustered macromolecules. A Lattice Boltzmann method (LBM) simulation was also developed to determine the effect of contact angle hysteresis and boundary conditions on the droplet dynamics.

FINDINGS

The two surface treatments were optimized to produce comparable water wetting characteristics. With a negative Gibbs free energy on the hydrophilic-half, the oil droplet receded to the hydrophobic-half. On the silanized surface, the droplet was pinned and the resultant droplet shape was a distorted spherical cap, having receded uniformly on the unmodified surface. Modifying the surface with clustered macromolecules, the droplet receded slightly to form a spherical cap. However, droplet recession was non-uniform and daughter droplets formed near the wettability boundary. The LBM simulation revealed that daughter droplets formed when θR > 164°, with the final droplet shape accurately described by imposing a diffuse wettability boundary condition.