Sustainable Multifunctional Clay–Polymer Hybrid Bricks Reinforced with Biochar and Metal Oxide Nanoparticles for Structural Strength, Thermal Regulation, and Indoor Air Purification
摘要
The construction sector accounts for a significant share of CO2 emissions, driving the adoption of low-carbon building materials that protect indoor air quality. Fired clay bricks are durable but require kiln energy and provide no active control of indoor VOCs. Unfired clay composites that unify load-bearing capacity, low thermal conductivity, and photocatalytic VOC removal remain under-validated. This study developed and evaluated an unfired clay–PVA–biochar–TiO2 hybrid brick for structural, thermal, and air-purifying functions. Mixtures with 10 wt.% PVA, 10 wt.% biochar, and 2 wt.% TiO2 were molded and humidity/oven-cured without firing; fired and additive-only controls were prepared. Strength, density, ASTM C67 water uptake/porosity, thermal conductivity, and UV-A chamber formaldehyde decay were measured; SEM/EDS and FTIR/XRD verified additive integration. The hybrid brick maintains masonry-grade strength; compressive strength was measured at 10.2 ± 0.5 MPa, compared with 15.0 ± 0.5 MPa for fired clay, while bulk density was reduced from 1.85 to 1.58 g/cm3. Heat transfer was reduced; thermal conductivity was reduced from 0.80 to 0.40 W/(m·K), and 24 h water absorption was reduced from 12.0 ± 0.7% to 6.3 ±y was reduced from 1.85 to 1.58 g 0.5%, indicating a 50% decrease in conductivity and a halved water uptake. Photocatalytic degradation was observed; formaldehyde concentration decreased by 25% from ~ 1.0 to ~ 0.75 ppm over 3 h under UV-A. These results support low-cost masonry units that reduce energy demand for firing, provide twice the thermal resistance compared to fired clay, and may reduce VOC concentrations through adsorption–photocatalysis. Future research will test durability under humidity cycling, evaluate performance under indoor lighting spectra, and quantify removal under sustainable industrialisation.