Micro and Nanoporous Membrane Platforms for Carbon Neutrality: Membrane Gas Separation Prospects.

Recently, carbon neutrality has been promoted as a potentially practical solution to global CO2 emissions and increasing energy-consumption challenges. Many attempts have been made to remove CO2 from the environment to address climate change and rising sea levels owing to anthropogenic CO2 emissions. Herein, membrane technology is proposed as a suitable solution for carbon neutrality. This review aims to comprehensively evaluate the currently available scientific research on membranes for carbon capture, focusing on innovative microporous material membranes used for CO2 separation and considering their material, chemical, and physical characteristics and permeability factors. Membranes from such materials comprise metal-organic frameworks, zeolites, silica, porous organic frameworks, and microporous polymers. The critical obstacles related to membrane design, growth, and CO2 capture and usage processes are summarized to establish novel membranes and strategies and accelerate their scaleup.

Biogenic Salvia species synthesized silver nanoparticles with catalytic, sensing, antimicrobial, and antioxidant properties.

Salvia (Lamiaceae family) is used as a brain tonic to improve cognitive function. The species including S. plebeia and S. moorcroftiana are locally used to cure hepatitis, cough, tumours, hemorrhoids, diarrhoea, common cold, flu, and asthma. To the best of authors' knowledge, no previous study has been conducted on synthesis of S. plebeia and S. moorcroftiana silver nanoparticles (SPAgNPs and SMAgNPs). The study was aimed to synthesize AgNPs from the subject species aqueous and ethanol extracts, and assess catalytic potential in degradation of standard and extracted (from yums, candies, and snacks) dyes, nitrophenols, and antibiotics. The study also aimed at AgNPs as probe in sensing metalloids and heavy metal ions including Pb2+, Cu2+, Fe3+, Ni2+, and Zn2+. From the results, it was found that Salvia aqueous extract afforded stable AgNPs in 1:9 and 1:15 (quantity of aqueous extract and silver nitrate solution concentration) whereas ethanol extract yielded AgNPs in 1:10 (quantity of ethanol extract and silver nitrate solution concentration) reacted in sunlight. The size of SPAgNPs and SMAgNPs determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were 21.7 nm and 19.9 nm, with spherical, cylindrical, and deep hollow morphology. The synthesized AgNPs demonstrated significant potential as catalyst in dyes; Congo red (85 %), methylene blue (75 %), Rhodamine B (<50 %), nitrophenols; ortho-nitrophenol (95-98 %) and para-nitrophenol (95-98 %), dyes extracted from food samples including yums, candies, and snacks. The antibiotics (amoxicillin, doxycycline, levofloxacin) degraded up to 80 %-95 % degradation. Furthermore, the synthesized AgNPs as probe in sensing of Pb2+, Cu2+, and Fe3+ in Kabul river water, due to agglomeration, caused a significant decrease and bathochromic shift of SPR band (430 nm) when analyzed after 30 min. The Pb2+ ions was comparatively more agglomerated and chelated. Thus, the practical applicability of AgNPs in Pb2+ sensing was significant. Based on the results of this research study, the synthesized AgNPs could provide promising efficiency in wastewater treatment containing organic dyes, antibiotics, and heavy metals.

Removal of Brilliant Green Dye from Water Using Ficus benghalensis Tree Leaves as an Efficient Biosorbent.

The presence of dyes in water stream is a major environmental problem that affects aquatic and human life negatively. Therefore, it is essential to remove dye from wastewater before its discharge into the water bodies. In this study, Banyan (Ficus benghalensis, F. benghalensis) tree leaves, a low-cost biosorbent, were used to remove brilliant green (BG), a cationic dye, from an aqueous solution. Batch model experiments were carried out by varying operational parameters, such as initial concentration of dye solution, contact time, adsorbent dose, and pH of the solution, to obtain optimum conditions for removing BG dye. Under optimum conditions, maximum percent removal of 97.3% and adsorption capacity (Qe) value of 19.5 mg/g were achieved (at pH 8, adsorbent dose 0.05 g, dye concentration 50 ppm, and 60 min contact time). The Langmuir and Freundlich adsorption isotherms were applied to the experimental data. The linear fit value, R2 of Freundlich adsorption isotherm, was 0.93, indicating its best fit to our experimental data. A kinetic study was also carried out by implementing the pseudo-first-order and pseudo-second-order kinetic models. The adsorption of BG on the selected biosorbent follows pseudo-second-order kinetics (R2 = 0.99), indicating that transfer of internal and external mass co-occurs. This study surfaces the excellent adsorption capacity of Banyan tree leaves to remove cationic BG dye from aqueous solutions, including tap water, river water, and filtered river water. Therefore, the selected biosorbent is a cost-effective and easily accessible approach for removing toxic dyes from industrial effluents and wastewater.

Progress in microbial fuel cell technology for wastewater treatment and energy harvesting.

The global energy crisis has stimulated the development of various forms of green energy technology such as microbial fuel cells (MFCs) that can be applied synergistically and simultaneously toward wastewater treatment and bioenergy generation. This is because electricigens in wastewater can act as catalysts for destroying organic pollutants to produce bioelectricity through bacterial metabolism. In this review, the factors affecting energy production are discussed to help optimize MFC processes with respect to design (e.g., single, double, stacked, up-flow, sediment, photosynthetic, and microbial electrolysis cells) and operational conditions/parameters (e.g., cell potential, microorganisms, substrate (in wastewater), pH, temperature, salinity, external resistance, and shear stress). The significance of electron transfer mechanisms and microbial metabolism is also described to pursue the maximum generation of power by MFCs. Technically, the generation of power by MFCs is still a significant challenge for real-world applications due to the difficulties in balancing between harvesting efficiency and upscaling of the system. This review summarizes various techniques used for MFC-based energy harvesting systems. This study aims to help narrow such gaps in their practical applications. Further, it is also expected to give insights into the upscaling of MFC technology while assisting environmental scientists to gain a better understanding on this energy harvesting approach.

ZnO-ZnTe hierarchical superstructures as solar-light-activated photocatalysts for azo dye removal.

The excessive amount of textile effluents disposed into the water streams is a common source of contamination of the hydrosphere. To efficiently remove pollutants in water bodies, there is growing demand for highly efficient, cost effective, and green remediation techniques. In line with such demand, a heterostructured photocatalyst (ZnO-ZnTe) has been prepared through the assembly of zinc oxide (ZnO) and zinc telluride (ZnTe). A synergistic interaction between surface adsorption and photocatalysis was explored for the removal of azo dye using a hierarchical superstructure under solar-light irradiation. Methylene blue (MB) was bleached by about 91% under visible irradiation for 2 h to support the role of the prepared heterostructures as effective photocatalysts (QY is 3.16 × 10-7 molecules/photon). Moreover, the kinetic reaction rate of ZnO-ZnTe superstructures was 19.0 µmol g-1 h-1, which was 1.54 and 1.97 times higher than those of pristine ZnO and ZnTe, respectively. These results may be ascribed to the presence of a common cation that may have helped in the diffusion of photogenerated electrons between ZnO and ZnTe, while efficiently suppressing the recombination frequency of photogenerated electrons and holes.

Upscaling feasibility of a graphite-based truncated conical microbial fuel cell for bioelectrogenesis through organic wastewater treatment.

In this research, efforts were put to demonstrate synergistic interactions between bioenergy generation and wastewater treatment. The extent of such synergistic effect was assessed against wastewater effluents released from the beverage industry through the operation of a membrane-less truncated conical (TC) microbial fuel cell (MFC). A graphite-based reactor was operated for five cycles in batch mode using beverage industry wastewater as an organic substrate. Maximum bioelectricity produced on the fifth operating cycle corresponded to a voltage of 338 mV and a power of 1.14 mW at 100 Ω. The MFC recorded a higher substrate degradation rate (0.84 kg of chemical oxygen demand [COD]/m3-day) accompanied by the development of an electroactive biofilm and polarization behavior (e.g., a reduction in internal resistance from 323 Ω to 197 Ω over five operation cycles). Cyclic voltammetry showed a maximum performance of the biofilm during the fifth cycle (through its enrichment) as interpreted by oxidation and reduction currents of 2.48 and -2.21 mA, respectively. The performance of the proposed MFC was superior to other designs reported previously in both effluent treatment and bioenergy generation. A maximum treatment efficiency of 84.4% (in 385 h) was seen at an organic load (COD) of 3500 mg/L with the specific power yield (0.504 W/Kg of substrate (COD) removal) and volumetric power yield (15.03 W/m3). Our experimental studies support that the proposed system could be upscaled to realize the commercial operation.

Study on Direct Synthesis of Energy Efficient Multifunctional Polyaniline-Graphene Oxide Nanocomposite and Its Application in Aqueous Symmetric Supercapacitor Devices.

The synthesis of promising nanocomposite materials can always be tricky and depends a lot on the method of synthesis itself. Developing such synthesis routes, which are not only simple but also can effectively catch up the synergy of the compositing material, is definitely a worthy contribution towards nanomaterial science. Carbon-based materials, such as graphene oxide, and conjugative polymers, such as conductive polyaniline, are considered materials of the 21st century. This study involves a simple one pot synthesis route for obtaining a nanocomposite of polyaniline and graphene oxide with synergistic effects. The study was carried out in a systematic way by gradually changing the composition of the ingredients in the reaction bath until the formation of nanocomposite took place at some particular reaction parameters. These nanocomposites were then utilized for the fabrication of electrodes for aqueous symmetric supercapacitor devices utilizing gold or copper as current collectors. The device manifested a good capacitance value of 264 F/g at 1 A/g, magnificent rate performance, and capacitance retention of 84.09% at a high current density (10 A/g) when gold sheet electrodes were used as the current collectors. It also showed a capacitance retention of 79.83% and columbic efficiency of 99.83% after 2000 cycles.

Achieving Ultrahigh Cycling Stability and Extended Potential Window for Supercapacitors through Asymmetric Combination of Conductive Polymer Nanocomposite and Activated Carbon.

Conducting polymers and carbon-based materials such as graphene oxide (GO) and activated carbon (AC) are the most promising capacitive materials, though both offer charge storage through different mechanisms. However, their combination can lead to some unusual results, offering improvement in certain properties in comparison with the individual materials. Cycling stability of supercapacitors devices is often a matter of concern, and extensive research is underway to improve this phenomena of supercapacitive devices. Herein, a high-performance asymmetric supercapacitor device was fabricated using graphene oxide-polyaniline (GO@PANI) nanocomposite as positive electrode and activated carbon (AC) as negative electrode. The device showed 142 F g-1 specific capacitance at 1 A g-1 current density with capacitance retention of 73.94% at higher current density (10 A g-1). Most importantly, the device exhibited very high electrochemical cycling stability. It retained 118.6% specific capacitance of the starting value after 10,000 cycles at 3 Ag-1 and with coulombic efficiency of 98.06 %, indicating great potential for practical applications. Very small solution resistance (Rs, 0.640 Ω) and charge transfer resistance (Rct, 0.200 Ω) were observed hinting efficient charge transfer and fast ion diffusion. Due to asymmetric combination, potential window was extended to 1.2 V in aqueous electrolyte, as a result higher energy density (28.5 Wh kg-1) and power density of 2503 W kg-1 were achieved at the current density 1 Ag-1. It also showed an aerial capacitance of 57 mF cm-2 at current 3.2 mA cm-2. At this current density, its energy density was maximum (0.92 mWh cm-2) with power density (10.47 W cm-2).

Fabrication of Eco-Friendly Solid-State Symmetric Ultracapacitor Device Based on Co-Doped PANI/GO Composite.

An eco-friendly solid-state symmetric ultracapacitor (Uc) device was fabricated using a polyaniline graphene oxide composite co-doped with sulfuric acid (H2SO4) and dodecyl benzene sulfonic acid (DBSA) or camphor sulfonic acid (CSA), as electrode material utilizing gold sheets as current collectors. The device showed specific capacitance value of 150 F/g at 1 A/g current density, with a capacitance retention value of 93.33% at higher current density (10 A/g), indicating a high rate capability. An energy density of 15.30 Whkg-1 with a power density of 1716 Wkg-1 was obtained at the current density of 1 A/g. The values of areal capacitance, power density, and energy density, achieved at the current density of 5 mAcm-2, were 97.38 mFcm-2, 9.93 mWhcm-2, and 1.1 Wcm-2, respectively. Additionally, the device showed very low solution and charge transfer resistance (0.885 Ω and 0.475 Ω, respectively). A device was also fabricated utilizing copper as current collector; however, a lower value of specific capacitance (82 F/g) was observed in this case.