Efficient biogas upgrading requires the removal of CO₂ and H₂S to produce biomethane suitable for downstream applications. Geopolymer-based materials have attracted interest because their aluminosilicate structures can be tailored through precursor composition, activation, curing, and secondary-phase incorporation, while waste-derived precursors offer opportunities for resource valorization. This review critically evaluates geopolymer-based CO₂/CH₄ separation and H₂S capture and examines their potential integration into a single membrane platform. The literature provides limited direct evidence of CO₂/CH₄ separation using geopolymer membranes, whereas CO₂/CH₄ adsorption selectivity has been demonstrated in geopolymer-based materials, and H₂S capture has primarily been investigated using particulate or bulk geopolymer sorbents. However, the available literature has yet to establish the integrated performance of a single geopolymer membrane for CO₂/CH₄ separation and H₂S removal under mixed CO₂/CH₄/H₂S feeds. Consequently, the existing evidence remains fragmented across adsorption, gas permeation, and H₂S sorption studies. Key research gaps include establishing the relationship between adsorption properties and membrane-level separation, controlling selective-layer thickness and defects, elucidating gas transport mechanisms, and validating performance under humid, multicomponent conditions. The review also examines membrane architecture, functionalization, composite design, and emerging metal–organic framework (MOF) and covalent organic framework (COF) systems to identify relevant design principles. Altogether, integrated CO₂/CH₄/H₂S purification using geopolymer membranes remains largely at the proof-of-concept stage. Future research should prioritize mixed-gas testing, H₂S breakthrough and regeneration studies, interface engineering, and standardized transport measurements.
Certain cyanobacterial species can transfer photosynthetically generated electrons to extracellular electrodes, enabling light-driven photocurrent generation and offering potential applications in sustainable bioelectricity generation and solar fuel production. However, intracellular competition for photosynthetically generated electrons and inefficient extracellular electron transfer (EET) limit photocurrent generation and its utilisation for hydrogen production. To overcome these limitations, various strategies have been explored, including the addition of exogenous redox mediators and physical or genetic modification of cyanobacterial cells. Here, we demonstrate hydrogen production driven by mediator-free photocurrent generated by wild-type Synechocystis sp. PCC 6803 and investigate the associated metabolic costs. Using a dual-chamber photo(bio)electrochemical system (PES), we examine how the applied anode potential influences photocurrent generation, cathodic hydrogen evolution and cellular metabolism.. Applying an anode potential of 1.0 V (vs. Ag/AgCl) resulted in photocurrent densities of up to 2.1 ± 0.09 mA cm⁻², enabling biohydrogen production at a rate of 0.154 ± 0.006 m³ m⁻² d⁻¹ with a Faradaic efficiency of 90 ± 4% under the tested operating conditions. Over 24 h, the system passed a cumulative charge of 441 C and released 48.5 ± 2.1 mL of hydrogen, compared with 109 C and 11.5 ± 0.7 mL when suspended cells were omitted, and 12 C with no cells present. Electrochemical analyses revealed enhanced redox activity and improved electron-transfer kinetics across repeated operational cycles, indicating strong biofilm–electrode interactions. The imposed voltage enhanced microbial metabolism, increasing ATP production and single-cell protein productivity. However, the study was limited to 24 h batch operation, with photocurrent declining after ~2 h; long-term stability and scale-up remain to be demonstrated. These findings demonstrate that controlled electrochemical bias can effectively re-route photosynthetic electrons toward electrochemical outputs for sustainable hydrogen generation and bio-based manufacturing.
The utilization of waste animal fats as biodiesel feedstock offers a sustainable alternative to conventional vegetable oils, particularly in regions where palm oil production competes with food resources. This study investigates the production and characterization of biodiesel synthesized from beef tallow and lard through alkali-catalyzed transesterification using methanol and sodium hydroxide. The produced fatty acid methyl esters (FAMEs) were purified through liquid–liquid extraction and subsequently characterized using FTIR and ¹H NMR spectroscopy, gas chromatography, and physicochemical analyses. Biodiesel conversion achieved 97.3% for beef tallow and > 99% for lard with good-isolated yields 72% and 82%, respectively. The main fatty acids identified were palmitic, stearic, and oleic acids, while lard biodiesel contained a higher proportion of monounsaturated FAMEs. Key fuel characteristics such as viscosity, cetane number, density, and acid value, complied with ASTM D6751, EN 14214, and Indonesian National Standards, although cloud and pour points were slightly elevated due to saturated fat content. This study establishes that high-quality biodiesel can be efficiently produced from animal fats, offering a sustainable alternative to palm oil in Indonesia's renewable energy sector.
This study focuses on the development of a green bio-adsorbent based on a bacterial cellulose (BC) film derived from waste nata de coco , an abundant and sustainable source of bacterial cellulose, utilized as a bio-based functional trunk material for the removal of Cs(I) ions from aqueous solutions. BC film was modified via simultaneous gamma radiation–induced graft polymerization, an environmentally friendly and initiator-free technique for interfacial surface engineering, with glycidyl methacrylate (GMA) as grafting monomer. The optimum grafting condition was achieved at GMA concentration of 4% v/v and radiation dose of 20 kGy. Subsequently, the grafted BC was functionalized with iminodiacetic acid (IDA), resulting in an IDA group density of approximately 1.5 mmol g⁻ 1 , yielding the final bio-adsorbent denoted as BC- g -PGMA/IDA. The adsorption performance of BC- g -PGMA/IDA toward Cs(I) ions was systematically evaluated and compared with that of a synthetic counterpart, PE/PP- g -PGMA/IDA. The BC-adsorbent exhibited adsorption performance, achieving a maximum adsorption capacity of 3 mg g⁻ 1 at an initial Cs(I) concentration of 10 mg L⁻ 1 . Kinetic analysis indicated pseudo-first-order adsorption behavior controlled by external mass transfer. The reusability of the adsorbent was also evaluated over ten cycles, demonstrating stable performance with an adsorption efficiency remaining above 91 ± 1.87% throughout the cycles. The results demonstrate that BC- g -PGMA/IDA is an efficient and environmentally friendly bio-adsorbent with strong potential for practical applications in Cs(I) removal from contaminated water.
This study focuses on the development of a green bio-adsorbent based on a bacterial cellulose (BC) film derived from waste nata de coco, an abundant and sustainable source of bacterial cellulose, utilized as a bio-based functional trunk material for the removal of Cs(I) ions from aqueous solutions. BC film was modified via simultaneous gamma radiation–induced graft polymerization, an environmentally friendly and initiator-free technique for interfacial surface engineering, with glycidyl methacrylate (GMA) as grafting monomer. The optimum grafting condition was achieved at GMA concentration of 4% v/v and radiation dose of 20 kGy. Subsequently, the grafted BC was functionalized with iminodiacetic acid (IDA), resulting in an IDA group density of approximately 1.5 mmol g⁻1, yielding the final bio-adsorbent denoted as BC-g-PGMA/IDA. The adsorption performance of BC-g-PGMA/IDA toward Cs(I) ions was systematically evaluated and compared with that of a synthetic counterpart, PE/PP-g-PGMA/IDA. The BC-adsorbent exhibited adsorption performance, achieving a maximum adsorption capacity of 3 mg g⁻1 at an initial Cs(I) concentration of 10 mg L⁻1. Kinetic analysis indicated pseudo-first-order adsorption behavior controlled by external mass transfer. The reusability of the adsorbent was also evaluated over ten cycles, demonstrating stable performance with an adsorption efficiency remaining above 91 ± 1.87% throughout the cycles. The results demonstrate that BC-g-PGMA/IDA is an efficient and environmentally friendly bio-adsorbent with strong potential for practical applications in Cs(I) removal from contaminated water.
