Unraveling the photocatalytic and antimicrobial performance of carbon-TiO2/lignin hybrid admixtures in sustainable cement composites

Abstract

The primary objective of this study was to develop cement composites with the ability to photocatalytically degrade contaminants and exhibit antimicrobial properties. To achieve this, titanium(IV) oxide was modified with carbon to create a photocatalyst active under both UV and visible light. The modified TiO₂ was then combined with kraft lignin, a byproduct of paper production, resulting in functional inorganic-organic hybrid systems. These hybrid materials were characterized using various research methods, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), low-temperature nitrogen sorption, and X-ray diffraction (XRD). The photocatalytic activity of these materials was evaluated under UV and visible light. The pristine components and resulting hybrid systems were incorporated into cement composites as admixtures in the amount of 1.0 wt% relative to the cement weight. The performance of both fresh and cured cement mortar was assessed, focusing on workability, compressive and flexural strength after 3 and 28 days of hydration. The compressive strength after 28 days in the case of the most favorable cement mortars improves from 54.7 MPa, as obtained for the reference sample, to values exceeding 60.0 MPa. It was established that the presence of lignin in the hybrid material introduced into the cement mortar contributes to an improvement in workability, ranging from 10 to 15 mm. Additional evaluations included pore structure parameters using mercury intrusion porosimetry, microstructural properties, photocatalytic activity as well as antimicrobial efficacy. The results indicated that the newly developed carbon-TiO₂/kraft lignin hybrid systems can be effectively utilized as functional admixtures in cement composites, enhancing their photocatalytic and antimicrobial properties.