Surface modification of toner-based recyclable iron oxide self-doped graphite nanocomposite to enhance methylene blue and tetracycline adsorption.

An innovative task was undertaken to convert ubiquitous and toxic electronic waste, waste toner powder (WTP), into novel adsorbents. Alkaline modification with KOH, NaOH, and NH4OH was employed for the first time to synthesize a series of surface-modified WTP with enhanced dispersibility and adsorption capacity. XRD, XRF, FTIR, and BET analyses confirmed that the prepared KOH-WTP, NaOH-WTP, and NH4OH-WTP were oxygen-functionalized self-doped iron oxide-graphite nanocomposites. The prepared adsorbents were used to remove methylene blue and tetracycline from aqueous solutions. KOH-WTP (0.1 g/100 mL) adsorbed 80% of 10 mg/L methylene blue within 1 h, while 0.1 g/100 mL NH4OH-WTP removed 72% of 10 mg/L tetracycline in 3 h. Exploring surface chemistry by altering solution pH and temperature suggested that hydrogen bonding, electrostatic interactions, π-π electron stacking, and pore filling were plausible adsorption mechanisms. Scanning electron microscopy revealed a diminishing adsorbents porosity after adsorption proving the filling of pores by the adsorbates. KOH-WTP and NH4OH-WTP removed 77% and 61% of methylene blue and tetracycline respectively in the fourth reuse. The adsorption data of methylene blue and tetracycline fitted the Freundlich isotherm model. The maximum adsorption capacities of KOH-WTP and NH4OH-WTP for methylene blue and tetracycline were 59 mg/g and 43 mg/g respectively. The prepared adsorbents were also compared with other adsorbents to assess their performance. The transformation of waste toner powder into magnetically separable oxygen-functionalized WTP with outstanding recyclability and adsorption capacity showcases a significant advancement in sustainable wastewater treatment. This further aligns with the principles of the circular economy through the utilization of toxic e-waste in value-added applications. Additionally, magnetic separation of surface-modified WTP post-treatment can curtail filtration and centrifugation expenses and adsorbent loss during wastewater treatment.

Catalytic fabrication of graphene, carbon spheres, and carbon nanotubes from plastic waste.

In this study, we reported sustainable and economical upcycling methods for utilizing plastics such as polyethylene terephthalate (PET) and polypropylene (PP) compiled from the garbage of a residential area as cheap precursors for the production of high-value carbon materials such as graphene (G), carbon spheres (CS), and carbon nanotubes (CNTs) using different thermal treatment techniques. Graphene, carbon spheres, and carbon nanotubes were successfully synthesized from PET, PP, and PET, respectively via catalytic pyrolysis. XRD and FTIR analyses were conducted on the three materials, confirming the formation of carbon and their graphitic structure. TEM images displayed uniform and consistent morphological structures of the fabricated materials. EDX data confirmed that the prepared carbon-based materials only contained carbon and oxygen without any significant contaminations. XPS results revealed significant peaks in the C 1s spectra associated with sp2 and sp3 hybridized carbon for the three materials. BET spectra showed that the prepared CNTs (54.872 m2 g-1) have the highest surface area followed by carbon spheres (54.807 m2 g-1). The thermal stability of graphene surpassed both carbon spheres and carbon nanotubes which is mainly attributed to the stronger inter-molecular bonds of graphene. Based on the characterization of the prepared materials, these materials are promising to be utilized in environmental remediation applications due to their high carbon content, low cost, and high surface area.

Effective degradation of tetracycline via persulfate activation using silica-supported zero-valent iron: process optimization, mechanism, degradation pathways and water matrices.

Pure zero-valent iron (ZVI) was supported on silica and starch to enhance the activation of persulfate (PS) for tetracycline degradation. The synthesized catalysts were characterized by microscopic and spectroscopic methods to assess their physical and chemical properties. High tetracycline removal (67.55%) occurred using silica modified ZVI (ZVI-Si)/PS system due to the improved hydrophilicity and colloidal stability of ZVI-Si. Incorporating light into the ZVI-Si/PS system improved the degradation performance by 9.45%. Efficient degradation efficiencies were recorded at pH 3-7. The optimum operating parameters determined by the response surface methodology were PS concentration of 0.22 mM, initial tetracycline concentration of 10 mg/L, and ZVI-Si dose of 0.46 g/L, respectively. The rate of tetracycline degradation declined with increasing tetracycline concentration. The degradation efficiencies of tetracycline were 77%, 76.4%, 75.7%, 74.5%, and 73.75% in five repetitive runs at pH 7, 20 mg/L tetracycline concentration, 0.5 g/L ZVI-Si dose, and 0.1 mM PS concentration. The degradation mechanism was explained, and sulfate radicals were the principal reactive oxygen species. The degradation pathway was proposed based on liquid chromatography-mass spectroscopy. Tetracycline degradation was favorable in distilled and tap water. The ubiquitous presence of inorganic ions and dissolved organic matter in the lake, drain, and seawater matrices interfered with the tetracycline degradation. The high reactivity, degradation performance, stability, and reusability of ZVI-Si substantiate the potential practical application of this material for the degradation of real industrial effluents.

Green valorization of end-of-life toner powder to iron oxide-nanographene nanohybrid as a recyclable persulfate activator for degrading emerging micropollutants.

The sustainable management of toner waste (T-raw) was performed via carbonization at 500 °C (T-500) and 600 °C (T-600) to produce iron oxide-nanographene nanohybrid (FeO-NG) for activating persulfate (PS) to efficiently degrade dyes (methylene blue, MB), antibiotics (sulfamethazine, SMZ), and pesticides (diazinon, DZN). Morphology, crystallinity, chemical structure, chemical composition, surface area, and pore size distribution of the synthesized materials were investigated using various analyses. High degradation ratios of MB were attained over a wide pH range (2-7), and the optimum operating conditions were determined. The FeO-NG/PS system was tested in different water matrices. MB degradation efficiency dropped from 80.13% to 78.56% after five succeeding experiments, proving the high stability of T-500. Trapping experiments proved the major role of sulfate radicals and the minor contribution of singlet oxygen. The toxicity evaluation of the treated and untreated MB solutions was conducted via measuring the cell viability, showing an increase in cell viability ratio after the degradation of MB. The degradation efficiencies of DZN and SMZ were 97.54% and 83.7%, respectively and the mineralization ratios were 74.08% and 60.37% at initial concentrations of sulfamethazine and diazinon of 50 and 100 mg/L, respectively. The high degradation efficiency of emerging micropollutants as well as the inexpensiveness, and facile synthesis of the catalyst boost the prospect of applying the proposed system on an industrial scale.

Utilization of iron waste from steel industries in persulfate activation for effective degradation of dye solutions.

The performance of three solid iron wastes (SIW-1, SIW-2 and SIW-3) was evaluated as an activator of persulfate (PS) for the degradation of methylene blue (MB). SIW-3 showed the highest performance among the three catalysts. The morphology, chemical composition and chemical structure of the three SIW were investigated using various analyses. Complete degradation of methylene blue (MB) in neutral pH was achieved after 60 min at PS concentration of 4 mM, initial MB concentration of 10 mg/L and catalyst dose of 1.0 g/100 mL using light. The degradation efficiency of MB decreased from 100% to 34.6% by increasing the initial MB concentration from 10 mg/L to 100 mg/L. The degradation of MB followed the second-order model. Scavenging experiments showed the major role of hydroxyl and sulfate radicals in the MB degradation. The performance of iron waste in the retained form was investigated and the degradation efficiencies were 96%, 91.2%, 91%, 89% and 86% in five succeeding cycles at pH 7, catalyst dose of 1 g/100 mL, initial MB concentration of 10 mg/L and PS concentration of 4 mM. Moreover, the reusability of suspended iron waste was investigated. The degradation efficiencies of methylene blue, methyl red, Congo red and acid blue-25 were 100%, 97%, 96% and 97.3%, respectively after 60 min. The degradation pathways of MB were proposed after the identification of intermediates using liquid chromatography-mass spectroscopy analysis. This study revealed that the iron waste can be efficiently employed for PS activation in the suspended and immobilized modes which reduces the total cost of the Fenton process paving the way for the large-scale application of this technique.