Photocatalytic Based Degradation Processes of Lignin Derivatives

Table 2

Summary of starting conditions for the photocatalytic degradation of lignin.

Reference	Lignin source	Catalyst	Reaction conditions
MacHado et al. [42]	Peroxyformic acid lignins from eucalyptus grandis wood (EL1); EL1 + sodium borohydride	TiO2 and H2O2	Lignin concentration: 0.25 mg/mL, °C, pH 11, UV Vis radiation  nm, 400 W mercury lamp, cylindrical Pyrex glass reactor, constant oxygen bubbling
Ksibi et al. [47]	Water soluble lignin obtained from black liquor	TiO2-P25 (Degussa)	Lignin concentration: 90 mg/L, °C, pH 8.2, UV-radiation  nm, pyrex reactor open to air, Philips HPK 125 W lamp
Kansal et al. [48]	Lignin from wheat straw kraft digestion	TiO2-P25 (Degussa) and ZnO	Lignin concentration: 10–100 mg/L in 100 mL, ZnO catalyst dose (0.5–2.0 g/L), pH of the solution (pH 3–11), solar illumination, oxidant concentration:  M to  M, thin bed film slurry pond reactor, oxidant: sodium hypochlorite solution (4% available Cl2)
Dahm and Lucia [49]	Whitewater from industrial process water that exits in paper machines	Fischer Scientific rutile TiO2	Lignin concentration: 40 mg/L in 500 mL batch reactor, °C–42°C, Rayonet photochemical chamber, 16 VWR 8-W black light, phosphor (350-nm) lamps, constant oxygen bubbling, power of illumination: 128 to 64 W, light intensity: 223–445 mW/cm^3
Portjanskaja and Preis [50]	Lignin, purchased from Aldrich	TiO2 P25-N (Degussa)	Lignin concentration: 100 mg/L, pH 8, batch reactor system, reactor open to air, Phillips TLD 15 W/05 low-pressure luminescent mercury UV-lamp, UV-radiation  nm, power density of irradiation = 0.7 mW/cm^2, visible light source
Tanaka et al. [51]	Lignin from coniferous wood	TiO2 (TiO2—TP-2 of Fujititan)	Lignin concentration: 0.003 to 0.03%, UV-radiation  nm, cylindrical reaction vessel
Tonucci et al. [33]	Ca^2+ and lignin derivatives	TiO2 as Degussa P25; + polyoxometalates (POM), H2O2	Open quartz tubes (20 mL) reactor, °C, 1 atm, multirays of ten UV lamps of 15 W power each, UV-radiation  nm
Miyata et al. [24]	Picea glehnii wood flour	TiO2/polyethylene oxide (PEO)	Reactor: open petri dish, °C,  h, 400 W mercury lamp
Shende et al. [17]	Kraft lignin	TiO2-ZnO-ZrO2	Lignin concentration: 1 mg/mL in 10 mL, 250 W Xenon lamp and AM 1.5 G lamp filter, power density of irradiation: 100 mW/cm^2, solar lamp simulator
Tian et al. [52]; and Pan et al. [53]	Kraft lignin from black liquor	Ta2O5-IrO2 and PbO2 thin film; TiO2 nanotube/PbO2	Lignin concentration: 30% (w/w), UV-radiation  nm,  min, power density of irradiation: 20 mW/cm^2, blue wave TM50 AS UV spot lamp, EG&G 2273 potentiostat/galvanostat to apply current, Ti/TiO2NT/PbO2 electrode as working electrode and Pt coil as outer electrode and Ag/AgCl as reference electrode
Awungacha Lekelefac et al. [54], [55]	Lignin sulfonate from paper waste water	TiO2 as Degussa P25; TiO2 from sol-gel process of TiOSO4, TTIP	Lignin concentration: 500 mg/L in 200 mL, Osram Planon light source, irradiance: 30–40 W/m^2, UV-radiation λ: 280–420 nm,  h, reactor open to air, recirculation system, flow rate 22.5 mL/min