Lignocellulosic Biomass Waste-Derived Cellulose Nanocrystals and Carbon Nanomaterials: A Review.

Rapid population and economic growth, excessive use of fossil fuels, and climate change have contributed to a serious turn towards environmental management and sustainability. The agricultural sector is a big contributor to (lignocellulosic) waste, which accumulates in landfills and ultimately gets burned, polluting the environment. In response to the current climate-change crisis, policymakers and researchers are, respectively, encouraging and seeking ways of creating value-added products from generated waste. Recently, agricultural waste has been regularly appearing in articles communicating the production of a range of carbon and polymeric materials worldwide. The extraction of cellulose nanocrystals (CNCs) and carbon quantum dots (CQDs) from biomass waste partially occupies some of the waste-recycling and management space. Further, the new materials generated from this waste promise to be effective and competitive in emerging markets. This short review summarizes recent work in the area of CNCs and CQDs synthesised from biomass waste. Synthesis methods, properties, and prospective application of these materials are summarized. Current challenges and the benefits of using biomass waste are also discussed.

Defect-Engineered Nanostructured Ni/MOF-Derived Carbons for an Efficient Aqueous Battery-Type Energy Storage Device.

A Ni-based metal-organic framework (Ni-MOF) has been synthesized using a microwave-assisted strategy and converted to nanostructured Ni/MOF-derived mesoporous carbon (Ni/MOFDC) by carbonization and acid treatment (AT-Ni/MOFDC). The materials are well characterized with Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET), revealing that chemical etching confers on the AT-Ni/MOFDC-reduced average nanoparticle size (high surface area) and structural defects including oxygen vacancies. AT-Ni/MOFDC displays low series resistances and a higher specific capacity (C s) of 199 mAh g-1 compared to Ni/MOFDC (92 mAh g-1). This study shows that the storage mechanism of the Ni-based electrode as a battery-type energy storage (BTES) system can be controlled by both non-faradic and faradic processes and dependent on the sweep rate or current density. AT-Ni/MOFDC reveals mixed contributions at different rates: 75.2% faradic and 24.8% non-faradic contributions at 5 mV s-1, and 34.1% faradic and 65.9% non-faradic at 50 mV s-1. The full BTES device was assembled with AT-Ni/MOFDC as the cathode and acetylene black (AB) as the anode. Compared to recent literature, the AT-Ni/MOFDC//AB BTES device exhibits high energy (33 Wh kg-1) and high power (983 W kg-1) with excellent cycling performance (about 88% capacity retention over 2000 cycles). This new finding opens a window of opportunity for the rational designing of next-generation energy storage devices, supercapatteries, that combine the characteristics of batteries (high energy) and supercapacitors (high power).