The major requirements for accelerating the process of anaerobic digestion and energy production are breaking the structure of waste activated sludge (WAS), and transforming it into a soluble form suitable for biodegradation. This work investigated and analysed a novel bench-scale ultrasonic system for WAS disruption and hydrolysis using ultrasonic homogenization. Different commercial sonoreactors were used at low frequencies under a variety of operating conditions (intensity, density, power, sonication time, and total suspended solids) to evaluate the effects of the equipment on sludge hydrolysis and to generate new insights into the empirical models and mechanisms applicable to the real-world processing of wastewater sludge. A relationship was established between the operating parameters and the experimental data. Results indicated an increase in sonication time or ultrasonic intensity correlated with improved sludge hydrolysis rates, sludge temperature, and reduction rate of volatile solids (33.51%). It also emerged that ultrasonication could effectively accelerate WAS hydrolysis to achieve disintegration within 5–10 min, depending on the ultrasonic intensity. This study also determined multiple alternative parameters to increase the efficiency of sludge treatment and organic matter reduction, and establish the practicality of applying ultrasonics to wastewater sludge pretreatment.
Using bacterial cellulose (BC) prepared from Vietnamese nata-de-coco via an alkaline pre-treatment followed by a solvent exchange process, epoxy resin (EP)/BC biocomposites were fabricated using three different dispersion techniques: mechanical stirring only, both mechanical stirring and grinding, and both mechanical stirring and ultrasonication. The surface of BC was modiﬁed with a silane coupling agent to improve the chemical afﬁnity between BC and epoxy resin. The biocomposite materials comprising BC, epoxy resin, and methylhexahydrophthalic anhydride as a curing agent were obtained from hot curing processing. The morphology and mechanical properties such as fracture toughness, enhanced K values, and tensile and ﬂexural properties of the bio-based composites were compared with those of the virgin epoxy resin. The silane coupling agent had a vital role in improving the mechanical characteristics of the bio-based composites. For instance, K IC values, tensile strength, Young’s modulus, and ﬂexural strength of the 0.3 wt% BC/epoxy composites with the presence of 2.0 wt% silane coupling agent were 0.7740 MPa m -1/2 , 53.32 MPa, 1.68 GPa, and 83.05 MPa. These values represent improvements of 36.77, 17, 15.86, and 14.42%, respectively, compared to a neat epoxy resin. Scanning electron microscopy revealed the rough fracture surface of epoxy resin/BC-based biocomposites with a multipathway crack, requiring more energy before breakage.
As a green ﬁller comprising both nano and micro-sized ﬁbrils, micro/nano white bamboo ﬁbrils (MWBFs) were treated with a silane coupling agent (S-MWBFs) prior to their introduction in an epoxy resin (EP). The sequential processes of steam explosion, alkaline treatment, and micro grinding were used to prepare to MWBFs. The effects of the S-MWBFs on various characteristics of the cured EP such as compatibility, fracture toughness, morphology, mechanical property, and ﬂame retardation were studied. The fracture toughness and mechanical characteristics of both the storage modulus and tand maximum increased following addition of the S-MWBFs to the EP. Notably, the fracture toughness of the EP with 0.3 wt% of S-MWBFs was 22.2% higher than that of unmodiﬁed resin. Scanning electron microscopy presented somewhat rougher surfaces with shear deformation and tortuously twisting cracks, resulting in a higher fracture toughness in S-MWBFmodiﬁed epoxy samples. However, ﬁre testing showed that the presence of S-MWBFs increased the burning rate of the EP.
In this study, Pt nanoparticles are deposited on the surface of nitrogen-sulfur functionalized reduced graphene oxide and mixed with double wall carbon nanotubes (Pt/NS-rGO/DWCNT). The obtained nanocomposite is used as an electrocatalyst for the ethanol electro-oxidation reaction (EOR). CO oxidation studies with differential electrochemical mass spectroscopy (DEMS) show a lower onset potential indicating higher poisoning tolerance of these materials. The electrocatalytic activity of the Pt/NS-rGO/DWCNT nanocomposite is studied at different temperatures (40, 50, 60, and 70 °C) and compared with that of Pt/rGO, Pt/rGO/DWCNT composites and commercial carbon-supported Pt catalyst. Pt/rGO/DWCNT and Pt/NS-rGO/DWCNT display significantly higher ethanol electro-oxidation currents especially at low potentials relevant to fuel cell applications. At high temperatures (>50 °C), Pt/NS-rGO/DWCNT is the most active catalyst in concordance with its higher apparent activation energy. Pt/NS-rGO/DWCNT is also the most durable of the catalysts after a 500 potential cycle test and suffers the least from poisoning effects during chronopotentiometric testing. These results allow to conclude that combining NS-functionalized graphene catalyst support with DWCNT to form a composite provides excellent performances due to enhanced Pt electrocatalytic activity from NS-functionalization and enhanced mass transfer from the DWCNT filler.
In this study, a new method for preparation of cross-linked magnetic chitosan particles (MCPs) from steel slag and shrimp shells using green tea extract as crosslinking reagent has been presented. The MCPs obtained were characterized by means of X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy and magnetic properties, and then were used to investigate the adsorption properties of Cu(II) and Ni(II) ions in aqueous solutions. The inﬂuence of experimental conditions such as contact time, pH value, adsorbent dose and initial metal concentration, and the possibility of regeneration were studied systematically. The Cu(II) and Ni(II) adsorption isotherms, kinetics and thermodynamics have been measured and discussed. The results show that the synthesized MCPs have high adsorption capacity for both metal ions (126.58 mg/g for Cu(II) and 66.23 mg/g for Ni(II)), and have excellent regeneration stability with efﬁciency of greater than 83% after five cycles of the adsorption–regeneration process. The adsorption process of Ni(II) and Cu(II) on MCPs was feasible, spontaneous and exothermic, and better described by the Langmuir model and pseudo-second-order kinetic equation. The MCPs can be applied as a low cost and highly efficient adsorbent for removal of heavy metals from wastewater due to its high adsorption capacity, easy recovery and good reusability.
Graphene has attracted widespread attention for supercapacitor applications thank to their excellent conductivity, mechanical flexibility, chemical stability and extremely high specific surface area. Here, all-graphene-oxide-supercapacitors were developed from two reduced graphene oxide (rGO) films as electrodes and one graphene oxide (GO) film as separator. The supercapacitors were then treated with 4M sulfuric acid at temperatures around 80 °C. By this treatment, the sulfuric acid molecules were physically intercalated into both rGO and GO films, which were confirmed by significant decrease intensity of characteristic peaks of sulfuric acid in Raman spectra. These sulfuric-acid-intercalated GO films can function as both quasi-solid-state electrolytes and separators. The average capacitance values measured at 100 mV s−1 of the thermally wetted supercapacitor at 84 °C is improved 93.7 times higher than that of the as-prepared all-graphene-oxide-supercapacitor. The maximum capacitance of 266 F cm−3 is obtained at scan rate 10 mV s−1 for the thermally wetted supercapacitor at 84 °C. To the best of our knowledge, this is the highest specific capacitance that has ever been reported for a graphene oxide-based supercapacitor. Importantly, being in a quasi-solid-state, the energy storage performance of supercapacitors are persistent over several thousand cycles, making it very much unlike other carbon-based supercapacitors.
Transparent and flexible energy storage devices have garnered great interest due to their suitability for display, sensor and photovoltaic applications. In this paper, we report the application of aerosol synthesized and dry deposited single-walled carbon nanotube (SWCNT) thin films as electrodes for an electrochemical double-layer capacitor (EDLC). SWCNT films exhibit extremely large specific capacitance (178 F g−1 or 552 μF cm−2), high optical transparency (92%) and stability for 10 000 charge/discharge cycles. A transparent and flexible EDLC prototype is constructed with a polyethylene casing and a gel electrolyte.
A novel photo-curable polyurethane resin for stereolithography has been demonstrated herein. The resin was printed by stereolithography to form 3-dimensional elastomeric objects without need of any diluent. The resultant elastomer exhibited good mechanical strength, high elasticity, and excellent cell adhesion and proliferation.