Carbon soot with arbitrary wettability deposited on solid surface by ethanol flame method

Synthesis of Carbonaceous Hydrophobic Layers through a Flame Deposition Process

In this study we report the effect of fuel type (biodiesel vs. methane), flame structure and flame height (inner-cone vs. outer-cone), and the percent of oxygen content in the oxidizer stream for the formation of hydrophobic carbon layers using co-flow diffusion flames. It was found that a flame formed using a gaseous fuel (methane) over a vaporized liquid fuel, Canola Methyl Ester (CME), has significant structural differences that enable vastly different deposition behavior of soot layers on the surface of solid substrates. Due to its larger pyrolysis zone (taller inner-cone), the CH4/air flame has a smaller region that supports uniform soot deposition of hydrophobic carbon layers (C-layers) compared to the CME/air flame. When a solid substrate is placed within the pyrolysis zone (inner-cone) of a flame the resulting layer is non-uniform, hydrophilic, and consists of undeveloped soot. However, when outside the pyrolysis zone, the deposited soot tends to be uniform and mature, ultimately creating a hydrophobic C-layer consisting of the typical microscale interconnected weblike structures formed of spherical soot nanoparticles. The effect of oxygen content (35% and 50% O2) in the oxidizer stream for the formation of hydrophobic C-layers was also studied in this work. It was found that oxygen enrichment within the CME flame alters the structure of the flame, hence affecting the morphology of the formed C-layer. Under oxygen enrichment the central region of the deposited C-layer is composed of a weblike structure similar to those seen in the air flames; however, this central region is bordered by a region of densely compacted soot that shows signs of significant thermal stress. At 35% O2 the thermal stress is expressed as multiple microscale cracks while at 50% O2 this border region shows much larger cracks and macroscale layer peeling. The formed C-layers under the different flame conditions were tested for hydrophobicity by measuring the contact angle of a water droplet. The morphology of the C-layers was analyzed using scanning electron microscopy.

Superhydrophobic Candle Soot Coating Directly Deposited on Aluminum Substrate with Enhanced Robustness

In this study, superhydrophobic surfaces were developed by using a simple and environmentally friendly technique. The nano-network of candle soot (CS) as the byproduct of incomplete combustion of paraffin candle was directly coated onto both smooth and micro-rough aluminum (Al) substrates for various time periods of deposition. The simple technique of mechanical sanding was used to impart micro-rough structures onto Al substrates using different sandpaper grit sizes. The scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and X-ray diffraction (XRD) techniques were used to characterize the morphology and chemistry of the prepared surfaces. Wetting analysis of the prepared surfaces was performed by measuring both water droplet contact angle (CA) and sliding angle (SA). The prepared coatings showed superhydrophobic properties with high CAs and low SAs for CS surfaces coated on roughened Al substrates. Moreover, the robustness of the prepared surfaces was tested by continuous impingement of water droplets onto their surfaces from various heights. Post-testing wetting analysis showed that the micro-nano surfaces of candle soot coated on micro roughened Al substrates demonstrated improved robustness. These surfaces could be useful for self-cleaning, anti-corrosion and anti-icing applications.

Facile Preparation of a Carbon-Based Hybrid Film for Efficient Solar-Driven Interfacial Water Evaporation

Solar-driven interfacial water evaporation is one promising technology for seawater desalination and sewage purification because it offers a feasible and sustainable strategy to relieve global water scarcity. Herein, a novel hybrid film composed of recycled carbon soot and poly(vinyl alcohol) is developed by a very simple, green, and highly scalable "salt-assisted" assembling method. The hybrid film possesses characteristics with a porous structure, superhydrophilicity, ∼100% light absorption, and low thermal conductivity, which can effectively convert light into heat under solar illumination. Consequently, the hybrid film can achieve a photothermal conversion efficiency of 91.5% under a stimulated solar irradiation of 1 kW m^-2. Furthermore, the hybrid film can be applied for seawater desalination and dye wastewater purification. The findings of our work not only provide a new photothermal platform with high light-to-thermal conversion ability and good reusability but also open a new avenue for the applications of carbon soot-based hybrid films in solar-assisted water evaporation and sewage purification.