SIAM: Science and Innovation of Advanced Materials

Waterborne Silane/Polysiloxane Hydrophobic Coating for Stone-Built Cultural Heritage Conservation

Supapit Kongchan, Kamonwan Pacaphol, Duangdao Aht-Ong — Mon, 19 Jun 2023 00:00:00 +0700

Stone-built cultural heritage is historical evidence that represents past human events and activities. Therefore, it must be preserved for later generations since its deterioration would hardly be recovered to be the original. One of the effective ways to protect the stone-built cultural heritage from damaging factors is by applying a protective coating on the stone surface. This work aimed to prepare a waterborne protective coating with hydrophobic and self-cleaning properties. Tetraethoxysilane (TEOS) and hydroxy-terminated polydimethyl siloxane (PDMS-OH) were used to produce a protective coating due to their ability to form siloxane (Si-O-Si) bonds with inorganic substrates and to enhance a water-repellent property. The optimum weight ratio of TEOS:PDMS-OH at 80:20 was used to formulate this coating. The effect of TEOS/PDMS-OH mixture concentrations in a water medium on the properties of coated limestone substrates was studied by using coatings with different concentrations at 5, 10, 15, and 20 wt%. The TEOS/PDMS-OH coating with 5% and 10% concentrations showed good stability with no viscosity change for at least 2 months. The performance of the coated limestone was evaluated by water contact angle measurement, tape peel test, capillary water absorption, and dirt pick-up resistance test. The optimum TEOS/PDMS-OH concentration found was 10 wt% which showed significant improvement in hydrophobicity as evidenced by an increment of average water contact angle from 0° in the uncoated surface to 96° in the coated surface. The color difference (∆E*) was 1.21 and the gloss values slightly increased from 2.23 to 2.63 GU. Furthermore, the area after the peel test still maintained good hydrophobicity. The dirt pick-up resistance test revealed that the coating could protect the surface from dirt, while the uncoated surface was still covered with dirt. The results confirmed that the waterborne coating with 10 wt% TEOS/PDMS-OH is appropriate for limestone substrate protection.

In-situ Synthesis of Lignin/ZnO Composites from Black Liquor for UV-Resistant and Antioxidant Agents in Bioplastics

Kannika Pleejaroen, Doungporn Yiamsawas, Pakorn Opaprakasit — Sat, 24 Jun 2023 00:00:00 +0700

An in-situ method has been developed to prepare lignin/ZnO composites from soda black liquor of oil palm empty fruit bunches. This method offers a new route to reduce the preparation steps and waste associated with the process. The effects of the lignin/zinc ratio on structures and properties of the obtained lignin/ZnO composites were investigated. The composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray spectroscopy (EDX) analysis, Fourier transforms infrared (FTIR), and UV-Visible spectroscopy. The obtained lignin/ZnO composites were then employed as an additive in polylactic acid (PLA) films by solvent casting to enhance their UV-resistant and antioxidant properties. The PLA-based bio-composites exhibited excellent UV-resistant and antioxidant properties. The prepared lignin/ZnO composites, derived from the developed facile and low-cost process, eco-friendly, and sustainable methods may find useful applications, especially smart packaging and cosmetic applications.

Engineering Hierarchically Porous Carbon Using a Facile Process: Assessment for Green Electrodes

Sopon Butcha, Sanchai Prayoonpokarach, Pongtanawat Khemthong — Sat, 24 Jun 2023 00:00:00 +0700

Production of carbonaceous materials from waste biomass is currently gaining much attention in scientific community due to the encouragement towards a sustainable approach. However, severe pretreatment processes are still the main challenging tasks. Herein, water hyacinth (WH) is used as a precursor. Hydrothermal carbonization in acidic conditions followed by thermal activation was used for the pretreatment. A novel chemical activator CH₃COOK was employed and compared to traditional chemical activators such as ZnCl₂ and K₂CO₃. High surface areas and numerous micropores of synthesized carbons are found in ZnCl₂ activation, while carbon compounds produced from K₂CO₃ and CH₃COOK possess modest surface areas but hierarchically micro-meso-structured carbon. These findings demonstrate that the CH₃COOK could serve as both a reagent for acid-assisted hydrothermal carbonization and a doped chemical for thermal activation. The use of CH₃COOK is more ecologically and economically friendly, confirmed by reduced chemical usage and less produced wastewater. Furthermore, because the obtained carbons include a large number of nitrogen contents of around 2.0 wt%, these hierarchically porous carbons could enhance their performances as electrode materials in energy storage applications.

Keywords: Water hyacinth, Hydrothermal carbonization, Biomass conversion, Hierarchical porous carbon, Potassium acetate

Efficient Four-Terminal Perovskite/Silicon Tandem Solar Cells by Using an Anti-Reflective Polymer Film as an Intermediate Matching Layer

Wed, 05 Jul 2023 00:00:00 +0700

Perovskite/silicon tandem solar cell is a promising candidate for highly efficient photovoltaic technologies. The 4T perovskite/silicon tandem solar cell comprises individual sub-cells that require no current matching. However, an optical loss to the bottom cell is a major issue, which is caused by an air gap serving as an optical spacer layer between sub-cells. This air gap results in a reduction in performance. In this work, commercial polydimethylsiloxane (PDMS) [Sylgard®184] was used as an intermediate matching layer (IML) in the 4T perovskite/silicon tandem cells to eliminate the air-spacer layer and increase the efficient performance. The PDMS anti-reflective polymer film was sandwiched between the top and bottom cells. The process has the potential to significantly improve the current density of silicon bottom cell with an active area of ~0.96 cm² from 13.39 mA/cm² (without an IML) to 14.95 mA/cm² (with an IML). The calculating overall performance of 4T perovskite/silicon heterojunction tandem cells with an air gap and an IML were achieved a PCE of 20.77% and 21.57%, respectively.

Keywords: Air-spacer layer, Anti-reflective polymer film, Perovskite/silicon tandem solar cells, Polydimethylsiloxane

Development of Indium Tin Oxide Stack Layer Using DC and RF Sputtering for Perovskite Solar Cells

Thu, 13 Jul 2023 00:00:00 +0700

Indium tin oxide (ITO) films were used as transparent conductive oxide (TCO) layers in perovskite solar cells (PSCs). Generally, the commercial ITO film-coated glass substrate has good electrical properties and a film thickness of around 340 nm but low transmittance in long wavelength regions of 750-1200 nm. The enhancement of light transmittance by the ITO stack layer was developed. Direct current (DC) sputtering with the oxygen-argon (O₂-Ar) gas mixture deposited the first ITO layer on a soda-lime glass substrate. Radio frequency (RF) sputtering with the Ar gas deposited in the second ITO layer. By optimizing the deposition conditions, the ITO stack layer has a total film thickness of around 330 nm, with a higher light transmittance of about 24% in the wavelength range of 750-1200 nm compared to the reference ITO (commercial). By using the ITO stack layer as a substrate for perovskite solar cells, the ITO stack layer structure of the DC:RF (1:1) has the highest efficiency compared to ITO film deposited from DC, RF, and reference ITO, which mainly from the increasing short current density (J_sc) of the solar cell. Applying an ITO stack layer for a perovskite solar cell achieved a power conversion efficiency of 14.9%.

Keywords: Indium tin oxide, ITO stack layer, Perovskite solar cell