Rational Design of Multifunctional Nanocatalysts for Environmental Remediation and Energy Conversion Technologies
The discovery of efficient and sustainable carbon-based nanotechnologies to solve both the scarcity of drinking water and global energy crisis has become a paramount task in the last decades. Owed to the fast population growth and industrialization of the modern society, access to potable water and clean energy technologies is becoming very hard around the globe. Water pollutants have become a serious threat to the environment and ecology because of their toxic nature. Parallelly, the current hydrocarbon-based fuel industries are generating high levels of contamination across the planet, making imperative the development of cleaner energy technologies. In this regard, the utilization of carbon-based nanomaterials could facilitate the development of effective renewable nanotechnology that can provide potential solutions towards the wastewater treatment and clean energy technologies. This dissertation presents the synthetic routes to design novel carbon-based nanoheterostructures as well as their characterization and functional evaluation for water treatment processes and energy conversion reactions. In chapter 2, the synthesis and characterization of an ecofriendly, cheap and efficient biosorbent, sulfonated spent coffee waste (SCW-SO3H) for water remediation is reported. SCWSO3H was synthesized through introducing sulfonic acid polar functionalities over the polymeric biomass (cellulose and lignin) of the spent coffee waste (SCW) by a simple, facile and versatile method. ICP-OES, SEM-EDX, FT-IR, XPS, TGA, Raman and UV-Vis spectroscopy were used to analyze the developed SCW-SO3H biosorbent and its adsorption capacity towards the removal of different environmental pollutants. The chemically engineered biosorbent showed excellent pollutant removal capacity of 812 mg/g, 462 mg/g and 302 mg/g toward methylene blue, tetracycline and Cr (VI), respectively. The present study can provide a platform in developing new generation of eco-friendly, cost-effective and efficient biosorbent for environmental remediation. In chapter 3, the synthesis and development of nickel and copper-based nanocatalysts for NaBH4-mediated reduction of environmental pollutants is reported. To achieve this, metallic Ni and Cu nanoparticles-embedded carbon sheets, namely as C@Ni and C@Cu, are synthesized through annealing of Ni-BDC and Cu-BDC metal-organic frameworks (MOFs) under an argon atmosphere at 600 °C. Their catalytic performance was tested for the catalytic reduction of environmental pollutants such as 4-nitrophenol, methyl orange and methylene blue. The obtained results from the catalytic studies are comparable with previously reported many other noble metalbased and transition metal-based nanocatalysts. Moreover, the catalytic performance of the developed catalysts dropped slightly (<3-6%) upon five times of recycling and reusing, showing the highly stable nature of the developed magnetic C@Ni and C@Cu nanocatalysts. In chapter 4, a facile, green, cheap, scalable and environmentally benign synthetic methodology to fabricate a hierarchically porous carbon-encapsulated transition metal-based M@TP nanocatalysts (M= Cu, Ni, Fe and Co) using commercial tissue paper as a template is reported. The morphology, crystalline structure, chemical composition and textural properties of the as-synthesized M@TP nanocatalysts were thoroughly characterized. X-ray diffraction analysis confirmed the pure metallic phase of the synthesized nanocatalysts, whereas the transmission electron microscopic analysis revealed that the metal nanocatalysts are encapsulated inside the porous carbon matrix. The catalytic activity of the M@TP nanocatalysts was thoroughly investigated towards the degradation of Congo red dye from water via peroxymonosulfate activation. Remarkably, the catalytic studies revealed that the Co@TP-6 nanocatalyst was so far the most active catalysts for the degradation of CR allowing the degradation of 97.68% of CR in 30 min with a higher reaction rate constant of 0.109 min-1. Quenching tests suggested that the sulfate radicals are the dominant reactive species in the catalytic degradation process. Moreover, the Co@TP-6 nanocatalyst is very stable with a minimal activity loss after four cycling runs. In chapter 5, the synthesis of bimetallic nickel-copper (NiCu) alloy nanoparticles confined in a sp2 carbon framework that exhibits tri-functional catalytic properties towards hydrogen evolution (HER), oxygen reduction (ORR) and oxygen evolution (OER) reactions is reported. XPS analysis revealed that the binding energy for Ni 2p3/2 band of the Ni0.25Cu0.75/C nanoparticles was shifted ~three times compared to other bimetallic systems and this was correlated to the high electrocatalytic activity observed. Interestingly, the bimetallic Ni0.25Cu0.75/C catalyst surpassed the OER performance of RuO2 benchmark catalyst exhibiting a small onset potential of 1.44 V vs RHE and an overpotential of 400 mV at 10 mA·cm−2 as well as the electrochemical long-term stability of commercial RuO2 and Pt catalysts and kept at least 90% of the initial current applied after 20000s for the OER/ORR/HER reactions. This study reveals significant insight about the structure-function relationship for non-noble bimetallic nanostructures with multifunctional electrocatalytic properties. In chapter 6, the synthesis of a new class of hybrid 0D−2D heterostructures comprised of boron carbon nitride nanosheets (BCN NSs) and fullerene molecules (C60/F) that exhibit metalfree electrocatalytic properties for the hydrogen evolution/oxidation reactions (HER/HOR) and the oxygen evolution/reduction reactions (OER/ORR) is reported. The nanohybrid supramolecular material with 10 wt% of F in BCN NSs (10% F/BCN) exhibited the largest Raman and C1s binding energy shifts in XPS, which were associated with greater cooperativity interactions and enhancing the ET processes at the F/BCN interface. The 10% F/BCN showed the highest tetrafunctional catalytic performance, outperforming the OER catalytic performance of commercial RuO2 catalysts with a η10 of 390 mV and very competitive onset potential values of -0.042 V and 0.92 V vs RHE for HER and ORR, respectively, and a current density value of 1.47 mA·cm−2 at 0.1 V vs RHE with an ultralow ΔGH* value of -0.03 eV towards the HOR process. Additionally, the 10% F/BCN catalyst was also used as both cathode and anode in a water splitting device, delivering a cell potential of 1.61 V to reach a current density of 10 mA·cm−2. In chapter 7, a simple MOF-derived synthetic strategy to fabricate low-dimensional (LD) nanohybrids formed by 0D-ZrO2 NPs and heteroatom-doped 2D-carbon nanostructures is reported. The 2D platforms controlled the electronic structures of interfacial Zr atoms, thus producing an optimized electron polarization for BCN/ZrO2 nanohybrid. XPS and theoretical studies revealed the key role of the synergistic couple effect of B and N on the interfacial electronic polarization. The BCN/ZrO2 showed excellent bifunctional electrocatalytic activity, delivering η10 of 301 mV and E1/2 of 0.85 V vs RHE for OER and ORR, respectively, which are comparable to the state-of-the-art LD nanohybrids. This work establishes a new route to fabricate highly efficient multifunctional electrocatalysts by tuning the electronic polarization properties of 0D−2Delectrochemical interfaces.
Chemistry|Materials science|Inorganic chemistry|Hydrologic sciences
Ahsan, Ariful MD., "Rational Design of Multifunctional Nanocatalysts for Environmental Remediation and Energy Conversion Technologies" (2021). ETD Collection for University of Texas, El Paso. AAI28865599.