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This review aims to prospect the development and utilization of proton-conducting biopolymers as sustainable matters. Its focal point is a move to sustainable materials of environment-friendly alternatives to conventional plastics. The review explores the properties and development techniques related to proton conduction in biopolymers and highlights their practical applications. Proton conductivity, mechanical strength, thermal stability, and chemical compatibility are pivotal features for creating advanced materials where biomaterials offer a sustainable production pathway for such materials. Methods for enhancing these properties include blending with similar biomaterials, making chemical modifications, creating nanostructures, and employing hybrid fabrication techniques. Improved proton conductivity is possible by forming proton pathways, attributed to chains of water molecules. These enhanced conductive materials have applications in fuel cells, sensors, ion separation membranes, and biomedical devices. Nature-derived biomimetic materials may offer such adaptable solutions that could also be eco-friendly and support a circular economy. This study has implications for industry professionals and researchers in the fields of energy and consumer electronics, highlighting the potential of biopolymers as key elements in sustainable product development.

The industrial production of conifer seedlings in nurseries uses large amounts of fertilizers to ensure their proper growth and accurate nutrient status. However, inorganic nitrogen fertilization leads to nitrate leaching, which has negative environmental consequences. An alternative solution could be the use of controlled-release fertilizers that supply nutrients over longer periods and hence have a lower environmental impact. This study analysed the performance of a novel arginine–iron–hexametaphosphate complex on Scots pine (Pinus sylvestris) seedlings. The complex was characterized using a wide range of analytical tools, indicating that it is a precipitated complex rather than a crystalline compound. Plant growth on arginine–iron–hexametaphosphate was comparable to a commercial inorganic nitrogen controlled-release fertilizer but with significantly lower nitrate leaching. A nitrogen budget of seedlings and growth substrate showed that seedlings had acquired nitrogen in excess of the amount of nitrogen present at the start of the experiment, and this excess nitrogen was smaller in seedlings grown on the inorganic fertilizer. Measurements of acetylene reduction in seedlings indicated low but measurable rates of nitrogen fixation, potentially contributing to the excess nitrogen. Together, the results showed that the arginine–iron–hexametaphosphate complex is a good alternative to commonly used fertilizers and can contribute to sustainable seedling production.

The detailed ash transformation process during the combustion of agricultural biomass containing moderate to high amounts of P was studied in entrained flow conditions. The selected fuels were grass and brewer’s spent grain (BSG) containing a moderate and high amount of P in the fuel, respectively. The experiments were conducted in a lab-scale drop tube furnace at 1200 and 1450 °C. The residual chars, ashes, and particulate matter (PM) were collected and analyzed by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC), and CHN-analysis. Additionally, the obtained results were interpreted through thermodynamic equilibrium calculations (TECs). For both fuels, P was primarily identified in the residual coarse ash (>1 μm) fractions. In contrast, a minor to moderate amount of fuel inherent P was detected in the fine particulate (<1 μm) fraction at 1200 and 1450 °C, respectively. For grass, the retained P in the residual coarse ash fractions was mainly identified as amorphous K-Ca-Mg-rich phosphosilicate melt. These phosphosilicates were most likely formed through the initial formation of molten K-rich silicates, with subsequent incorporation of Ca, P, and Mg. For BSG, a P-Si-rich fuel with moderate to minor amounts of Ca, Mg, and K, most P was retained in a Ca-Mg-rich phosphosilicate melt, likely originating from phytate-derived Ca-Mg phosphates interacting with fuel-inherent Si-rich particles. The results obtained from this study could be used to address the ash-related challenges and potential P-recovery routes during pulverized fuel combustion of P-containing biomass.