Vinu R

The present study investigates the isotherm and kinetics of aqueous hexavalent chromium [Cr(VI)] removal using biochar (Ka-BC) and magnetic biochar (Ka-MBC) derived from seaweed biomass, Kappaphycus alvarezii. Characteristics of prepared Ka-BC and Ka-MBC were explored by FT-IR, XRD, SEM, EDAX, and surface area analysis. The effects of initial pH, contact time, and chromium concentration were investigated based on batch adsorption experiments. The maximum chromium adsorption was 64.8% and 82.5% using Ka-BC and Ka-MBC, respectively, corresponding to 500 mg/L loading at pH 3 with initial chromium concentration of 1 mg/L after 150 min of sorption reaction. The removal of chromium is mainly dependent on pH and follows a pseudo-second-order kinetic model. The adsorption experiments showed that Ka-MBC has better removal capacity than the Ka-BC due to multi-layer mechanism and surface roughness phenomenon in Ka-MBC. The chromium adsorption on Ka-MBC followed Langmuir isotherm. The current study demonstrates the utilization of seaweed-derived magnetic biochar composite as an efficient sorbent and low-cost alternative for the removal of Cr(VI) from the environment. Graphical abstract: [Figure not available: see fulltext.]

Pyrolysis of algae is a promising route to produce high quality bio-oil and renewable chemicals. Owing to its complex structural composition, multiple pseudo-components are required to describe its thermal decomposition in a wide temperature range and evaluate the reaction kinetics. In this study, the pyrolysis behavior of the microalga, Nannochloropsis oculata (N. oculata), was studied by means of a thermogravimetric analyzer at various heating rates. A four-parallel-reaction scheme characterizing the pyrolysis of carbohydrate, protein, lipid and the secondary decomposition of char was employed to model thermal degradation using distributed activation energy model (DAEM). The average and standard deviation of activation energy, pre-exponential factor, and composition of the model components for pyrolysis of N. oculata were estimated. The model mass loss and differential mass loss profiles matched well with the experimental data at different heating rates. Based on the model predictions, the decomposition of proteins, carbohydrates, lipids and char occurred in the temperature regimes of 200–450 °C, 200–300 °C, 400–500 °C, and 750–900 °C, respectively. To gain valuable insights on the pyrolysate composition at various temperature regimes, analytical pyrolysis-gas chromatography/mass spectrometry experiments were performed. Indole and phenol, aliphatic and aromatic hydrocarbons, and long chain oxygenates were observed as the major pyrolysates in the temperature regimes of 30–350 °C, 350–600 °C and 600–1000 °C, respectively.