Current trends in structural development and modification strategies for metal-organic frameworks (MOFs) towards photocatalytic H2 production: A review

Photocatalytic H₂ generation using semiconductor photocatalysts is considered as a cost-effective and eco-friendly technology for solar to energy conversion; however, the present photocatalysts have been recognized to depict low efficiency. Currently, porous coordination polymers known as metal-organic frameworks (MOFs) constituting flexible and modifiable porous structure and having excess active sites are considered to be appropriate for photocatalytic H₂ production. This review highlights current progress in structural development of MOF materials along with modification strategies for enhanced photoactivity. Initially, the review discusses the photocatalytic H₂ production mechanism with the concepts of thermodynamics and mass transfer with particular focus on MOFs. Elaboration of the structural categories of MOFs into Type I, Type II, Type III and classification of MOFs for H₂ generation into transition metal based, post-transition metal based, noble-metal based and hetero-metal based has been systematically discussed. The review also critically deliberate various modification approaches of band engineering, improvement of charge separation, efficient irradiation utilization and overall efficiency of MOFs including metal modification, heterojunction formation, Z-scheme formation, by introducing electron mediator, and dye based composites. Also, the MOF synthesized derivatives for photocatalytic H₂ generation are elaborated. Finally, future perspectives of MOFs for H₂ generation and approaches for efficiency improvement have been suggested.     

Electrophoretic deposition of graphene oxide on carbon brush as bioanode for microbial fuel cell operated with real wastewater

Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm^?2 to 381 mWm^?2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.     

Iron pyrite films prepared by sulfur vapor transport

Iron films deposited via thermal evaporation, with a thickness between 100 and 250 nm, were converted into FeS₂ by open sulfur transport using nitrogen as a gas vector. The films thus obtained constituted a single pyrite phase and were optically highly absorbing. The sulfurization process was optimized. As a result, sample temperature and conversion time were found to be the major determining parameters. The films were characterized using several methods. The crystallinity and phase identification were determined by X-ray diffractometry. Scanning electron microscopy showed a homogeneous surface of both iron and pyrite layers. Optical transmission measurements confirmed the highly absorbing character of FeS₂ and allowed the determination of direct (1.35 eV) and indirect (0.82 eV) transitions.     

Performance of the decorrelator receiver for DS-CDMA mobile radio system employing RAKE and diversity through Nakagami fading channel

Multiple-access interference (MAI) and multipath fading are two of the most significant factors limiting the capacity and performance of direct-sequence code-division multiple-access (DS-CDMA) systems. In this paper, synchronous multiuser receivers that combine antenna diversity, RAKE reception, and a multipath decorrelator for MAI cancellation are analyzed in a Nakagami faded environment using a maximal ratio combiner or a selection combiner. A coherent binary phase-shift keying employing DS-CDMA is considered. Arbitrary branch correlation is also considered for any diversity order in the case of identical severity fading on the branches.     

Effect of functional group of ferrocene redox substance on the transport properties of newly designed ion exchange membrane prepared from polymer gel

A different newly designed cationic exchange polymer membrane and anionic exchange polymer membrane were introduced, and also the transport properties of these polymeric membranes were investigated in this study. The transport properties of these polymer membranes in contact with ferrocene redox derivatives were estimated by using electrochemical techniques such as cyclicvoltammetry, chronopotentiometry, and chronoamperometry techniques, respectively. The used ferrocene redox substances, which have different functional groups, were (Ferrocenylmethyl) trimethylamonium iodide, FcMA, Ferrocenedimethanol, FcDM, and Ferrocene carboxylic acid, FcCA. It indicated that the performance of a membrane depended on the content of polymer gel, anionic exchange polymer site (20 wt % and 50 wt %) or cationic polymer exchange site (20 wt % and 50 wt %), and the efficiency of the functional groups of cationic and anionic exchange polymer site as well. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Water and salt permeability of reinforcement polymer‐gel composite membrane

The charged mosaic polymer membrane (CMM) without reinforcement and the composite charged mosaic polymer membrane (CCMM) with reinforcement were investigated in terms of salt and water transport (permeability). The composite charged mosaic polymer membrane (CCMM) with reinforcement showed a unique transport behavior such as preferential material transport L_p and ω. Water permeability coefficient, L_p and salt permeability coefficient, ω were estimated by taking account of active layer thickness of composite polymer gel. The L_p and ω values of CCMM with reinforcement were larger than those of CMM without reinforcement. On the other hand, the reflection coefficient of CCMM, σ, showed negative value, which suggested preferential material transport to solvent transport. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radiation polymerization of acrylonitrile in a viscous system with styrene

Radiation polymerization of acrylonitrile in a viscous system with styrene was performed at ambient temperature by using γ‐rays. It is found that the overall rate of polymerization was accelerated after critical conversion due to the gel effect. As the molar fraction of styrene in monomer feed (f_St) is increased, both the total polymer conversion and molar fraction of acrylonitrile in the copolymer feed (F_AN) were decreased. The monomer reactivity ratios for acrylonitrile and styerne were determined to be r₁ (AN) = 0.25 and r₂ (St) = 2.0, respectively. The copolymers obtained were characterized by Fourier transformed infrared spectra (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), ¹H‐NMR, and pyrolysis mass spectrometry (PMS). It was found that the slight addition of styrene to acrylonitrile strongly changes crystallinity, morphology, and thermal decomposition of the resulting polymer. ¹H‐NMR measurment of AN/St copolymer showed the appearance of aromatic proton signals and shifted the resonance of the methylene proton to lower chemical shifts. The mass spectra of AN/St copolymers showed fragments of pyrolysates corresponding to oligonitriles with styrene end groups. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 268–275, 2002; DOI 10.1002/app.10324     

Solar cookers for outdoors and indoors

The solar cooking process has been investigated to develop safe, simple, portable, and reliable solar cookers. The concept of insulated and vapor-tight pots has been introduced and applied to oven, point-focus and heat-pipe cookers. A new, flat-plate cooker with heat pipes has been developed. It requires no tracking and allows cooking to be done in the shade or indoors. Also, a novel-portable cooker, the Mina Oven, featuring a vapor-tight pot and an integral collector with reflector flaps, has been constructed and tested. A second portable cooker that has been developed is the Arafa Cooker, which comprises a parabolic dish focused at a glazed and insulated receiver. Experiments indicated that all cookers yielded satisfactory performance, with cooking times of 25–45 min per kg of food per m² of solar collection area while operating from 10 a.m. to 4 p.m.