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In this study, the effect of nanocellulose sulfonate group content on adsorption of an opioid simulant was tested. The opioid simulant used was Victoria blue R, an amine dye. Nanocellulose filters were fabricated by crosslinking cellulose nanocrystals (CNCs) with chitosan to improve the mechanical stability of freeze-dried CNCs. Thermogravimetric analysis confirmed the filter’s thermal stability and operating temperatures. Conductometric titration, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques were used to characterize the degree of nanocellulose functionalization. Lastly, the adsorption performance of the sulfonated nanocellulose filter was tested and fitted to kinetic models and adsorption isotherms. The adsorption of the dye by the sulfonated nanocellulose followed pseudo-second order kinetics and the Langmuir isotherm. The maximum adsorption of Victoria blue R dye by sulfonated nanocellulose (68.56 mg/g) is significantly higher than those of other adsorbents, like activated carbon (0.59-2.97 mg/g) and magnetic microparticles (40.98 mg/g). Thus, sulfonated cellulose nanocrystals are a promising material for the sequestration of opioids from water.

To tackle the ever-increasing demand for faster computation time and energy efficiency, analog neuromorphic architectures have been proposed in place of current artificial neural networks (ANNs) to emulate the computational abilities of the brain. Non-volatile, two terminal devices like memristors have been proven as viable candidates as an artificial synapse in these architectures. Presently, these devices are fabricated as crossbar, thin-film or nanowires. Nanowire-based architectures can play an important role in enhancing sparsity and randomness of a network, particularly when built using core-shell structures. We have previously shown that, depending on the forming process, a Pt core and HfO2 shell nanowire with a Ti top electrode can display eightwise (8W) or counter eightwise (C8W) bipolar resistive switching (BRS) at low potential ranges (±1 V). We will show that the symmetry of the core-shell nanowires combined with the 8W and C8W switching observed, are indicative of anti-serial memristor arrangement. Moreover, this configuration allows for the individual nanowires to exhibit complementary resistive switching (CRS) at higher potentials (±2 V). We will also show the current conduction mechanisms of this system, where thermionic emission dominates in the low resistance state while ohmic conduction dominates in the high resistance state, when the device is operated in BRS mode; and hopping conduction dominates in state 0 while space-charge-limited conduction dominates in state 1 when, the device is operated in CRS mode. When in BRS mode, the LRS and HRS states are stable for at least 1000 cycles and retain memory for 104 s. Finally, when testing for synaptic plasticity via long-term potentiation and depression (LTP and LTD), non-linear weight update behavior was observed. The effect of voltage pulse schemes on the synaptic response will be discussed in detail.

Highly dense, energy-efficient, and fast neuromorphic architectures emulating the computational abilities of the brain use memristors to emulate synapses in the analog or digital systems. Core–shell nanowires provide us with new opportunities for neuromorphic hardware integration. In this work, we have fabricated core–shell nanowires using a combination of bottom-up and top-down techniques. Additionally, we have demonstrated eightwise and counter-eightwise bipolar resistive switching (BRS). Remarkably, for the first time along with BRS, we have also demonstrated complementary resistive switching (CRS) in core–shell nanowires. Here, Pt was used as the conductive core and HfO2 as the memristive shell with Ti as the top electrode. The resistive switching properties were characterized by I–V curves and pulse operation modes. The cycling endurance in the BRS mode was 1000 cycles with an off–on ratio of ∼13 and resistance was retained for 104 s. Additionally, the compliance current used to form the nanowire in the BRS mode influenced the CRS operation by lowering the peak operating current. Additionally, current density–electric field analysis performed to determine charge conduction mechanisms revealed that the wires exhibit a thermionic emission mechanism in the high resistance state and Ohmic conduction mechanism in the low resistance state during the BRS mode of operation and hopping conduction mechanism in state 0 and space-charge-limited conduction mechanism in state 1 during the CRS mode of operation. This observed versatility in the mode of operation makes core–shell nanowires of significant interest for use as synaptic elements in neuromorphic network architectures.

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