Mohsin Nawaz

Graphene-based two-dimensional materials have been explored in a variety of applications, including the treatment of heavy-metal-rich water/wastewater. Ethylenediaminetetraacetic acid (EDTA)-functionalized magnetic chitosan (CS) graphene oxide (GO) nanocomposites (EDTA-MCS/GO) were synthesized using a reduction precipitation method and applied to the removal of heavy metals, such as Pb 2+ , Cu 2+ , and As 3+ , from aqueous solutions. The synthesized nanocomposite was characterized by FT-IR, XRD, SEM, MPMS, zeta-potential and BET analyses. The influence of various operating parameters, such as pH, temperature, metal ion concentration, and contact time on the removal of the metal ions, was investigated. Owing to the large specific surface area, hydrophilic behavior, and functional moieties, the magnetic nanocomposite demonstrated excellent removal ability with a maximum adsorption capacity of 206.52, 207.26, and 42.75 mg g À1 for Pb 2+ , Cu 2+ , and As 3+ , respectively. The equilibrium data was evaluated by Langmuir and Freundlich isotherms, while the heavy metal adsorption reaction kinetics was analyzed by Lagergren pseudo-first-order and pseudo-second-order kinetic models. The nanocomposite was reused in four successive adsorption–desorption cycles, revealing a good regeneration capacity of the adsorbent.

In this study, the three-dimensional (3D) reduced graphene oxide/TiO 2 (RGOT) aerogel was synthesized by a facile one-step hydrothermal treatment, and its photocatalytic efficiency was evaluated in the pho-todegradation of recalcitrant carbamazepine (CBZ) in aqueous solution. RGOT exhibited high adsorption and an almost twofold higher photodegradation ability than bare TiO 2 as more than 99% CBZ removal was observed within 90 min in 10 ppm aqueous solution of the latter. The mass ratio of TiO 2 in the RGOT aerogel substantially affected CBZ adsorption and photocatalytic degradation, with the optimal TiO 2 /GO ratio in RGOT found to be 2:1. The chemical bonding between TiO 2 and GO and the effective reduction of the latter during RGOT synthesis were also considered to achieve high photocatalytic efficiency, because the physical mixture of GO and TiO 2 showed a lower photocatalytic CBZ degradation ability than bare TiO 2. The macroporous 3D structure, abundant surface sites for anchoring the catalyst, effective charge separation, and mass transportation of CBZ near the photocatalyst surface are the attractive features of RGOT aerogels, promoting their use in resolving environmental issues.

The use of engineered nanomaterials is continuously increasing in commercial products and industrial applications, and a significant portion of these materials may enter domestic and industrial wastewater streams and subsequently, wastewater treatment plants. Microbial fuel cells (MFCs) represent a new emerging technology for simultaneously generating bioenergy and treating wastewater. In this work, the performance of a MFC with wastewater containing multi-walled carbon nanotubes (MWCNTs) was evaluated. No significant negative effect on power generation was observed for MWCNT concentrations from 10 mg L À1 to 200 mg L À1. In fact, there was a stimulating effect due to the increased conductivity resulting from the MWCNTs, therefore slightly enhancing voltage generation (linked to enhanced electron transfer rate). The maximum voltage generation was increased from 0.61 V to 0.68 V (at 1000 U external resistance). Low lactate dehydrogenase release at all concentrations of MWCNTs showed that no adverse cell piercing took place and the wrapping of cells by MWCNTs most likely occurred. Chemical oxygen demand (COD) removal efficiency was also enhanced from 74.2% to 84.7%. The experimental results demonstrated that wastewater containing MWCNTs can be applied to MFCs for generating bioelectricity and treating wastewater without any significant adverse effect on performance.

Microorganisms have the potential to become a game-changer in sustainable energy production in the coming
generations. Microbial fuel cells (MFCs) as an alternative renewable technology can capture bioenergy (electricity)
from carbon-based sources by utilizing microorganisms as biocatalysts. This study demonstrated that MFC
technology can be explored for bioelectricity production from orange peel waste (OPW), an agricultural
byproduct and an organic substrate, without any chemical pretreatment or the addition of extra mediators. A
maximum voltage generation of 0.59 ± 0.02 V (at 500 Ω) was achieved in a dual chamber MFC during stable voltage
generation stages. The maximum power density and current density obtained were 358.8 ± 15.6 mW/m2
and 847 ± 18.4 mA/m2
, respectively. Key components of OPW, namely pectin and cellulose, were also tested
in their pure form, with pectin giving a stable current, while no significant current generation was achieved
using cellulose alone as the substrate, thus demonstrating the absence of cellulose-degrading bacteria. Maximum
pectinase and polygalacturonase enzyme activities of 18.55 U/g and 9.04 U/g (per gram of substrate), respectively
were achieved during orange peel degradation in MFCs. Bacterial identification using 16S rRNA analysis of the initial
inoculum fed to the MFC, the biofilm attached to the anode, and the anode suspension, showed significant
diversity in community composition. A well-known exoelectrogen, Pseudomonas, was present among the predominant
genera in the anode biofilm.

Microbial fuel cells (MFCs) are envisaged as an emerging cost effective technology for organic waste
treatment and simultaneous bioelectricity generation. In this work, the potential use of lemon peel waste
for bioenergy generation was investigated in a dual chamber MFC. A stable voltage generation of
0.58 ± 0.02 V (500 U external resistor) at peel waste concentrations of 0.5e1.5 g l
1 was achieved. A
maximum power density of 371 ± 30 mW m
2
, corresponding to a current density of 994 ± 41 mA m
2
,
was obtained at an initial peel waste concentration of 1.0 g l
1
. Performance characteristics in terms of
coulombic efficiency and internal resistance obtained by the MFC at this initial concentration were 32.3%
and 143 U, respectively. The effect of sonication time, temperature, and external resistance were also
studied to determine the maximum level of cumulative power generation. These preliminary results
clearly indicate that the carbon source present in lemon peel waste can be utilized by exoelectrogens
present in the anodic chamber, and that it ultimately releases electrons, which results in the generation
of cell voltage.

ABSTRACT Microbial fuel cells (MFCs) are attaining great interests for simultaneous current generation and recalcitrant organic pollutants treatment. Earlier investigations have revealed barley brewery wastewater as a cheap carbon source for simultaneous electricity generation, chemical oxygen demand (COD) removal, and poly azo dye (Sirius Red) degradation in a dual chamber microbial fuel cell. The experimental results showed a stable voltage production of 0.39 ± 0.02 V (220 Ω external resistor) using brewery wastewater as a sole carbon source. The maximum power density achieved was 271 ± 21 mW/m2 at an initial brewery wastewater concentration of 1000 mg/L COD, with the addition of dye (100 mg/L). A decolorization efficiency of 67% was attained in the anode chamber, and COD removal was 90% and 78% for brewery wastewater before and after the addition of dye, respectively, in a 48-h batch studies. UV-vis, Fourier transform infrared confirmed that the azo bonds in the dye were cleaved during dye degradation. Gas chromatography-mass spectrometry showed sodium-4-aminoazobenzene-4′-sulfonate and 1-3-bis(2-aminonapthalen-6-yl) urea as the main metabolites after the decolorization of Sirius Red.

Surface modification of titanium dioxide (TiO 2) was carried out with salicylic acid (SA) to generate an efficient Pickering emulsion (PE)-based photocatalytic system. The PE was stabilized with 0.5 and 1.0 mg mL −1 of TiO 2 and SA-TiO 2 by using cyclohexane and a synthetic aqueous Direct Red 80 (DR 80) solution (0.4:1) as the oil and water phases, respectively. The photocatalytic activity of solution-dispersed TiO 2 was compared with that of the PE-based photocatalytic system for DR 80 degradation. In almost all PE-based photocatalytic systems, 100% color removal of DR 80 was observed within 15–60 min, compared to 76% and 100% color removal, achieved after 120 min, using 0.5 and 1.0 mg mL −1 solution-dispersed TiO 2 , respectively. The estimated reaction rates of the PE-based photocatalytic system, as calculated using the Langmuir–Hinshelwood kinetics model, were almost double to those obtained for solution-dispersed TiO 2. However, the addition of a free oil phase adversely affected the photocatalytic activity, and the lowest DR 80 degradation percentage was observed using 0.5 or 1.0 mg mL −1 TiO 2. The results demonstrated that a functional PE was successfully stabilized with SA-TiO 2 , and enhanced photocatalytic degradation of the azo dye was achieved in an effective and novel way.