Calcium peroxide/lignocellulose composites for controlled oxygen release in water

Developing strategies for the sustainable use of natural resources is a current demand. In this study, lignocellulosic fibers were extracted from coffee husks using NaClO (pH 11); the yield was 11.5 %, and its composition was 90.3 % of holocellulose and 3.3 % of lignin. The resulting gel-like material was used to prepare composite xerogels with CaO₂, which released O₂ into the medium upon hydrolysis in water. The kinetics of O₂ release from both the composite xerogels and CaO₂ microparticles were evaluated at pH 7.5 (buffer) and pH 5.0 (MilliQ® water). In the buffered system without N₂ purging, the initial burst release of O₂ from CaO₂ microparticles (2.19 mg L⁻¹) occurred at an initial rate (V₀) of 3.11 mg L⁻¹ min⁻¹, reaching a maximal O₂ concentration of 20 mg L⁻¹ within 39 min. In contrast, composite xerogels significantly mitigated this burst effect, reducing the V₀ to 0.0361 mg L⁻¹ min⁻¹ and achieving a peak O₂ concentration of 13.6 mg L⁻¹ over ∼10 h. Similar trends were observed under hypoxic conditions. At pH 5.0, the reaction was less favorable due to a rapid increase in pH to ∼11 as the reaction progressed. The impact of the composite xerogel and CaO₂ microparticles on Allium cepa root growth was also investigated as a proof of concept to evaluate whether the released O₂ could benefit a model organism. Compared to the control, total root length increased by 221 % and 109 % in the presence of composite xerogel and CaO₂ microparticles, respectively.