Diatoms Biomass as a Joint Source of Biosilica and Carbon for Lithium-Ion Battery Anodes

Microalgal biochar assisted simultaneous removal of particulate matter, formaldehyde, and total volatile organic compounds (TVOC's) from indoor air

Biochar-based materials for air treatment have gained significant attention for removing health-detrimental volatile organic compounds (VOCs) and particulate matter (PM) in indoor air settings. However, high turnaround time, multiple pretreatment processes involved, and high pore size and low surface area (>10 μm, <100 m2 g-1) of lignocellulosic feedstocks demand alternative biochar feedstock material. Considering this, we designed a simple first-of-its-kind indoor air scrubbing material using diatoms-enriched microalgae biochar. In the present study, the microalgae were cultivated on waste anaerobic digestate (biogas slurry) and were pyrolyzed at three different temperatures: 300 °C (BC300), 500 °C (BC500), and 700 °C (BC700). The BC500 and BC700 showed the highest removal efficiencies (99 %) for total volatile organic carbons (TVOCs) and formaldehyde (HCHO) at concentrations of 1.22 mg m-3 HCHO and 8.57 mg m-3 TVOC compared to 50% efficiency obtained with commercially available surgical, cloth, and N95 masks. The biochar obtained showed a high Brunauer-Emmett-Teller (BET) surface area of 238 m2 g-1 (BC500) and 480 m2 g-1 (BC700) and an average pore size of 9-11 nm due to the mesoporous characteristic of diatom frustules. The comparatively poor performance of BC300 was due to lower surface area (150 m2 g-1) arising from incomplete organic removal, as evidenced by FESEM-EDX and FTIR. The high removal efficiencies in BC500 and BC700 were also attributed to the presence of reactive functional groups such as -OH and R-NH2. Concurrently, the average particulate matter (PM10, PM2.5, and PM1) removal efficiency for BC500 and BC 700 ranged between 66 and 82.69 %. The PM removal performance of BC500 and BC700 was lower (15-20%) than commercially available masks. Overall, the present study highlights the importance of diatoms (reactive Si) present inside the pores of microalgal biochar for enhanced removal of PM, TVOCs, and HCHO at temperatures above 500 °C. This complete approach signifies a step towards establishing a self-sustainable and circular process characterized by minimal waste generation for indoor air treatment.

Developing a novel lithium-ion battery anode material via thiol functionalization of diatom frustules plus Ag modification

The biosilicification of diatoms allows for the customization of the synthesis of functionalized diatom frustules. The S active sites (-SH) on diatom frustules were created by adding the organic silicon sources tetramethoxysilane (TMOS) and (3-mercaptopropyl)trimethoxysilane (MPTMS). The mechanisms of adsorption-reduction and the indirect effects of S active sites on electrochemical performance were declared. The DBS@C-Ag-3 anode material sourced from the cultivation condition with a silicon source of TMOS:MPTMS = 3:1 shows the best comprehensive performance and delivers a discharge capacity of ∼660 mAh·g-1 after 1000 cycles at 1 A·g-1. The electrochemical performance of DBS@C-Ag anode materials is also found to be dominated by structure at high temperatures and conductivity at low temperatures. Such a diatom frustule structure with sulfhydryl functionalization is promising for anode materials, and it suggests a biological strategy for creating other electrode materials by modifying them with metals to improve electrochemical performances.

The Use of Diatoms in the Synthesis of New 3D Micro-Nanostructured Composites (SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs) Exhibiting an Intense Anti-Stokes Photoluminescence

New 3D micro-nanostructured composite materials have been synthesised. These materials comprise SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs, exhibiting strong upconversion luminescence. The synthesis was accomplished by metabolically doping diatom cells with neodymium and vanadium. Subsequently, the biomass of these doped diatoms was subjected to pyrolysis at 800 °C. The morphology, structure, and physicochemical properties of the doped diatom biomass as well as dried (SiO2/CaCO3/Corg/NdVO4NPs) and pyrolysed (SiO2/CaO/Corg/NdVO4NPs) samples were characterised using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), thermal analysis (TG), and fluorescence spectroscopy (FS). Studies have shown that the surface of diatom shells is covered with trigonal prismatic nanocrystallites (nanoparticles) of NdVO4 with dimensions of 30-40 nm, forming the crystallite clusters in the form of single-layer irregular flakes. The synthesised composites produced intense anti-Stokes fluorescent emission in the visible region under xenon lamp excitation in the near-infrared (λex = 800 nm) at room temperature in an ambient atmosphere. Such materials could be attractive for applications in solar spectrum conversion, optical sensing, biosensors, or photocatalysts.

Pyrolized Diatomaceous Biomass Doped with Epitaxially Growing Hybrid Ag/TiO2 Nanoparticles: Synthesis, Characterisation and Antibacterial Application

In the pursuit of innovative solutions for modern technologies, particularly in the design and production of new micro/nanostructured materials, microorganisms acting as "natural microtechnologists" can serve as a valuable source of inspiration. This research focuses on harnessing the capabilities of unicellular algae (diatoms) to synthesize hybrid composites composed of AgNPs/TiO₂NPs/pyrolyzed diatomaceous biomass (AgNPs/TiO₂NPs/DBP). The composites were consistently fabricated through metabolic (biosynthesis) doping of diatom cells with titanium, pyrolysis of the doped diatomaceous biomass, and chemical doping of the pyrolyzed biomass with silver. To characterize the synthesized composites, their elemental and mineral composition, structure, morphology, and photoluminescent properties were analysed using techniques such as X-ray diffraction, scanning and transmission electron microscopy, and fluorescence spectroscopy. The study revealed the epitaxial growth of Ag/TiO₂ nanoparticles on the surface of pyrolyzed diatom cells. The antimicrobial potential of the synthesized composites was evaluated using the minimum inhibitory concentration (MIC) method against prevalent drug-resistant microorganisms, including Staphylococcus aureus, Klebsiella pneumonia, and Escherichia coli, both from laboratory cultures and clinical isolates.

A novel effective bio-originated methylene blue adsorbent: the porous biosilica from three marine diatom strains of Nanofrustulum spp. (Bacillariophyta)

In the present paper, for the first time the ability of the porous biosilica originated from three marine diatom strains of 'Nanofrustulum spp.' viz. N. wachnickianum (SZCZCH193), N. shiloi (SZCZM1342), N. cf. shiloi (SZCZP1809), to eliminate MB from aqueous solutions was investigated. The highest biomass was achieved under silicate enrichment for N. wachnickianum and N. shiloi (0.98 g L-1 DW and 0.93 g L-1 DW respectively), and under 15 °C for N. cf. shiloi (2.2 g L-1 DW). The siliceous skeletons of the strains were purified with hydrogen peroxide and characterized by SEM, EDS, the N2 adsorption/desorption, XRD, TGA, and ATR-FTIR. The porous biosilica (20 mg DW) obtained from the strains i.e. SZCZCH193, SZCZM1342, SZCZP1809, showed efficiency in 77.6%, 96.8%, and 98.1% of 14 mg L-1 MB removal under pH 7 for 180 min, and the maximum adsorption capacity was calculated as 8.39, 19.02, and 15.17 mg g-1, respectively. Additionally, it was possible to increase the MB removal efficiency in alkaline (pH = 11) conditions up to 99.08% for SZCZP1809 after 120 min. Modelling revealed that the adsorption of MB follows Pseudo-first order, Bangham's pore diffusion and Sips isotherm models.

Removal of the Basic and Diazo Dyes from Aqueous Solution by the Frustules of Halamphora cf. salinicola (Bacillariophyta)

Industrial wastes with hazardous dyes serve as a major source of water pollution, which is considered to have an enormous impact on public health. In this study, an eco-friendly adsorbent, the porous siliceous frustules extracted from the diatom species Halamphora cf. salinicola, grown under laboratory conditions, has been identified. The porous architecture and negative surface charge under a pH of 7, provided by the various functional groups via Si-O, N-H, and O-H on these surfaces, revealed by SEM, the N₂ adsorption/desorption isotherm, Zeta-potential measurement, and ATR-FTIR, respectively, made the frustules an efficient mean of removal of the diazo and basic dyes from the aqueous solutions, 74.9%, 94.02%, and 99.81% against Congo Red (CR), Crystal Violet (CV), and Malachite Green (MG), respectively. The maximum adsorption capacities were calculated from isotherms, as follows: 13.04 mg g^-1, 41.97 mg g^-1, and 33.19 mg g^-1 against CR, CV, and MG, respectively. Kinetic and isotherm models showed a higher correlation to Pore diffusion and Sips models for CR, and Pseudo-Second Order and Freundlich models for CV and MG. Therefore, the cleaned frustules of the thermal spring-originated diatom strain Halamphora cf. salinicola could be used as a novel adsorbent of a biological origin against anionic and basic dyes.

Diatom Frustules Decorated with Co Nanoparticles for the Advanced Anode of Li-Ion Batteries

Silica is regarded as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, large volume variation and poor electrical conductivity are limiting factors for the development of SiO₂ anode materials. To solve this problem, combining SiO₂ with a conductive phase and designing hollow porous structures are effective ways. In this work, The Co(II)-EDTA chelate on the surface of diatom biosilica (DBS) frustules and obtained DBS@C-Co composites decorated with Co nanoparticles by calcination without a reducing atmosphere is first precipitated. The unique three-dimensional structure of diatom frustules provides enough space for the volume change of silica during lithiation/delithiation. Co nanoparticles effectively improve the electrical conductivity and electrochemical activity of silica. Through the synergistic effect of the hollow porous structure, carbon layer and Co nanoparticles, the DBS@C-Co-60 composite delivers a high reversible capacity of >620 mAh g^-1 at 100 mA g^-1 after 270 cycles. This study provides a new method for the synthesis of metal/silica composites and an opportunity for the development of natural resources as advanced active materials for LIBs.

Metabolically Doping of 3D Diatomaceous Biosilica with Titanium

Diatoms represent, in terms of species number, one of the largest groups of microalgae that have the ability to synthesize phenomenal mineral composites characterized by complex hierarchical structures. Their shells, called frustules, create intricately ornamented structures, reminiscent of the most sophisticated, natural mosaics. Ordinated pore systems perforate siliceous walls of the frustules with diameters ranging from nano to micro-scale, forming openwork three-dimensional silica structures. The use of these features is one of the main challenges in developing new technological solutions. In this study we assess the ability of selected diatom species (Pseudostaurosira trainorii) for metabolic insertion of soluble titanium from the culture medium into the structure of amorphous silica cell walls by its cultivation in laboratory conditions. The study is aimed at obtaining new and strengthening the already existing optical properties of diatomaceous biosilica. The physicochemical properties of the obtained materials have been studied using a series of instrumental methods.

Next-Generation Materials for Energy Storage and Conversion

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Nanostructured diatom earth SiO2 negative electrodes with superior electrochemical performance for lithium ion batteries

Diatomaceous earth (DE) is a naturally occurring silica source constituted by fossilized remains of diatoms, a type of hard-shelled algae, which exhibits a complex hierarchically nanostructured porous silica network. In this work, we analyze the positive effects of reducing DE SiO₂ particles to the sub-micrometer level and implementing an optimized carbon coating treatment to obtain DE SiO₂ anodes with superior electrochemical performance for Li-ion batteries. Pristine DE with an average particle size of 17 μm is able to deliver a specific capacity of 575 mA h g⁻¹ after 100 cycles at a constant current of 100 mA g⁻¹, and reducing the particle size to 470 nm enhanced the reversible specific capacity to 740 mA h g⁻¹. Ball-milled DE particles were later subjected to a carbon coating treatment involving the thermal decomposition of a carbohydrate precursor at the surface of the particles. Coated ball-milled silica particles reached stable specific capacities of 840 mA h g⁻¹ after 100 cycles and displayed significantly improved rate capability, with discharge specific capacities increasing from 220 mA h g⁻¹ (uncoated ball-milled SiO₂) to 450 mA h g⁻¹ (carbon coated ball-milled SiO₂) at 2 A g⁻¹. In order to trigger SiO₂ reactivity towards lithium, all samples were subjected to an electrochemical activation procedure prior to electrochemical testing. XRD measurements on the activated electrodes revealed that the initial crystalline silica was completely converted to amorphous phases with short range ordering, therefore evidencing the effective role of the activation procedure.

Diatomaceous earth SiO₂ anodes with superior electrochemical performance are obtained by ball milling, carbon coating and electrochemical activation of SiO₂ particles.