Particulate matter (PM) air pollution poses a risk to public health, especially in rapidly industrializing countries. One major way to protect individuals from PM exposure is to use fiber-based filters for indoor air purification. In this study, a new low pressure drop poly­(vinyl alcohol) (PVA)/cellulose nanocrystals (CNCs) composite nanofibrous filter was fabricated using electrospinning. This electrospun PVA/CNCs filter was demonstrated as an air filter for the first time. The CNCs not only contributed to the PVA/CNCs system as mechanical reinforcement agents but also increased the surface charge density of the electrospinning solution, thereby reducing fiber diameter. The thinner fibers reduced pressure drop significantly and increased the efficiency of PM removal. Our results indicate that high PM2.5 removal efficiency was achieved (99.1%) under extremely polluted conditions (PM2.5 mass concentration > 500 μg m–3) with low pressure drop (91 Pa) at an airflow velocity of 0.2 m s–1. Considering that PVA and CNCs are both nontoxic and biodegradable, this high-efficiency composite filter with low air resistance is environmentally friendly and shows promise in indoor air purification applications.

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Commercial nanodiamonds (NDs) are usually produced by detonation and chemical vapor deposition. While these methods normally require either the application of extreme temperatures/pressures or expensive and hazardous gaseous/ chemical precursors, in this study, NDs were produced on paper made from nanolignin/cellulose nanofibrils (LCNF) composite film by means of direct laser writing at ambient temperature and air pressure. The generation of NDs was found to depend largely on high laser power. Graphene nanoribbons and carbon nanoonions were obtained at lower laser power as acceptable products. As cellulose nanofibrils were unsuccessfully lased in this study, the effects of diverse components of LCNFs were investigated. Results showed that a suitable cellulose content in LCNFs can accelerate laser carbonization, while an excessive oxygen content component will lead to the combustion of LCNFs in air. Moreover, it was found that a higher lignin content was essential for the formation of NDs. Individual nanolignin particles were able to be converted into NDs. However, this lasing process needed a higher-power laser than that did that from LCNF. Considering the abundance and renewability of LCNFs, the direct laser writing technique provides a simple, inexpensive, and environmentally friendly method for the synthesis of NDs and the fabrication of paper-based carbon patterns from biomass, which is both inexpensive and readily available.

In this work, cellulose nanocrystals (CNCs) obtained by the acid hydrolysis of waste bamboo powder were used to synthesize cellulose nanocrystal-g-poly(acrylic acid-co-acrylamide) (CNC-g-P(AA/AM)) aerogels via graft copolymerization followed by freeze-drying. The structure and morphology of the resulting aerogels were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the CNC-g-P(AA/AM) aerogels exhibited excellent absorbent properties and adsorption capacities. Subsequent Pb(II) adsorption studies showed that the kinetic data followed the pseudo-second-order equation, while the adsorption isotherms were best described using the Langmuir model. The maximum Pb(II) adsorption capacity calculated by the Langmuir model reached up to 366.3 mg/g, which is a capacity that outperformed that of the pure CNC aerogel. The CNC-g-P (AA/AM) aerogels become structurally stable through chemical cross-linking, which enabled them to be easily regenerated in HCl solution and retain the adsorption capacity after repeated use. The aerogels were found to maintain 81.3% removal efficiency after five consecutive adsorption–desorption cycles. Therefore, this study demonstrated an effective method for the fabrication of an aerogel adsorbent with an excellent reusability in the effective removal of Pb(II) from aqueous solutions.

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This study demonstrates a new transformation path from lignin to graphene and nanodiamonds (NDs) by femtosecond laser writing in air at ambient temperature and pressure. Graphene nanoribbon rolls were generated at lower laser power. When the laser power was high, NDs could be obtained apart from graphene and onion-like carbon intermediates. These structures were confirmed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The effects of laser power and laser writing speed on the structure of laser-induced patterns were investigated. The results show that the laser power was more important than the writing speed for the synthesis of carbon nanoparticles, and high laser power contributed to enhanced electrically conductive performance. Therefore, the direct laser irradiation technique leads a simple, low-cost, and sustainable way to synthesize graphene and NDs and is promising for the fabrication of sensors and electric devices.