| Semiconductor-based photo-electro-catalysis has proven to be a promising avenue to address the ever-growing energy and environmental issues.The capability of a photo-electro-catalyst to directly utilize solar energy to stimulate chemical reactions and generate applicable energy has led to the advancement of various technologies including solar cells,and photo electrochemical cells.A major challenge in utilizing the full-potential of semiconductor based photo-electro-catalysts is to inhibit charge-carriers recombination while maintaining good compatibility between strong redox ability and light response window.To engineer such photocatalysts a superior combinations of materials with high catalytic characteristics and boosted photo-electro-catalytic activity are highly desirable.In this context,the first reports discuss the fabrication of nanohybrid composites consisting of layered double hydroxide(LDHs)with various other metal and metal oxide partners.An elaborate study was carried by synthesizing nineteen(19)new materials,in which seven were associated with Ni-Mn-LDH,while the rest were associated with TiO2.A complete characteristic profiling was carried out to reveal the morphological,structural and optical response capabilities of the designed nanocomposites.The photo-/electrocatalytic and photocatalytic characteristics of the fabricated materials were evaluated by testing their performance in hydrogen evolution reaction(HER),oxygen evolution reaction(OER)reaction and photo-degradation of toxic colored dyes.At first taking the advantage of layered electronic structures,the Ni-Mn-LDHs and layered g-C3N4 coupled via single-step hydrothermal technique at controlled temperature.The optimized nanohybrids demonstrates relatively higher electrocatalytic OER efficiency(JOER=10 mA cm-2)at over potential of 316 mV and HER efficiency was estimated to be JHER=60 mA cm-2 at-147 mV.While under illuminations,a significant decline in overpotential values to 296 mV and-126 mV respectively was observed at same current density.When tested for photocatalytic degradation,the said materials demonstrated excellent degradation capability towards Rhodamine B(RhB)with catalytic rate constant(k)of 0.313 min-1.The exuberant performance were noted to be linked with high visible light harvesting capability coupled with faster charge-transport characteristics offered by the synergic coupling of different constituents in nanohybrids.Contrary to this,the Ti02 based photo materials were also concern to the water oxidation and environmental pollution remediation.First Ti02 and BiOCl based nanohybrids(BiOCl/TiO2-g-C3N4)was used for water oxidation,while achieved slight less OER electrocatalytic activity(JOER=10 mA cm-2)with overpotential of 376 mV.Under illuminations,a shift to 366 mV was noted that prevailing the influence of light.Since,it is well-known fact that doping of material is an effective approach in tuning the photocatalytic characteristics of catalyst.In the next phase,Ti02 was modified with Si02,Ag and AgBr nano particles(NPs).The modification was achieved using micro emulsification succeeded by hydrothermal and calcination treatments.The obtained mesoporous structures were then utilized for the photo-degradation of methyl orange(MO)dye and aniline compound.Under optimum conditions,the synthesized product formed into small hollow spheres@large hollow spheres of silica-titania matrix with uniformly distributed Ag-AgBr NPs with major phase as anatase.At temperature above 600?,a phase shift to rutile phase was observed besides aggregation of decorated particles.The optimal sample has fabulous absorption of visible light with band gap energy(Eg=2.87 eV).The photo-activity was evaluated both in UV and visible light conditions.A rate constant(k)of 0.0306 and 0.0465 min-1 was obtained for the degradation of MO respectively.In case of aniline,0.0306 and 0.0091 min-1 was estimated under UV and visible conditions respectively.Keeping in view,the performance of g-C3N4 in case of nanohybrids,we further coupled Ti02 to g-C3N4 nano sheets to engineer a superior heterojunction system for efficient photo-catalytic activity.The coupling was achieved by one-pot micro-emulsification of bulk graphitic carbon nitrides(g-C3N4)and tetra butyl orthotitanate followed by hydrothermal and calcination treatments.This approach enabled fabrication of nanocomposites with reduced band gap energy(Eg=2.37 eV)and cavity based structural morphology.The designed nanocomposites were tested for photocatalytic activity against Methylene Blue(MB)and RhB.The optimized sample exhibited elevated photocatalytic degradation performance with rate constant(k)of 0.096 min-1 and 0.061 min-1 for MB and RhB respectively.This enhanced performance was attributed to efficient absorption capability and fast-charge transportation with reduced recombination.Since metallic nanoparticle is known to exhibit,localized surface plasmon resonance(LSPR)which could potentially provide hot-electrons that could participate in the photo-catalytic activity.The coupling of Ti02-g-C3N4 nanocomposite with metallic nanoparticles would be a viable option to achieve much enhanced photo-activity.Thus,in the next phase,Ti02-g-C3N4 was coupled with Ag,AgBr to produce a multi-component system.The composite was prepared using previously discussed emulsification approach succeeded by hydrothermal and calcination treatments.This composite was tested for its catalytic potential against MB and RhB.Contrary to Ti02-g-C3N4,the Ag-AgBr/Ti02-g-C3N4;demonstrate enhanced photo-activity with high reaction constants(k)of 0.150 and 0.121 min-1 respectively.The superior performance was concluded to contribute by LSPR effect of metallic NPs which acted as energy centers enhancing light absorption(Eg=2.0 eV)of the designed composites.Furthermore the interfacial electron transportation within Ag-AgBr-Ti02 and g-C3N4 and appropriate aligning of band potential ensure the fruitful transportation of charge carriers providing an excellent photocatalytic activity.The designed materials was noted to possess excellent photo-stability,where EPR results concluded the major role of holes,O2·-and ·OH radicals in photo degradation experiments.This thesis provides comprehensive details of designing photo-active composite materials that have the capability to perform relatively better than their individual counter-parts.The enhanced performance of the composites reflects their ability to be considered for practical applications in the area of energy production or photo-remediation.In general,the study not only contributes in exploring superior combinations but also serves a step forward in driving such material in commercial market. |
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