| | No. | Adsorbents | Optimized conditions | The maximum adsorption capacity (mg g-1) | References |
| | 1 | Green tea waste | pH of 2, contact time of 60 minutes, and initial Cr(VI) concentration of 100 mg L-1 | 33.9 | [17] | | 2 | Tea waste | pH of 3.9, adsorbent dosage of 6 g L-1, contact time of 240 minutes, and temperature of 303 K | 23.3-73.3 | [41] | | 3 | Bleached-tea waste | pH of 2, adsorbent dosage of 2.5 g L-1, contact time of 24 hours, and initial Cr(VI) concentration of 100 ppm | 80 | [42] | | 4 | Black tea waste | pH of 10 and adsorbent dose of 14 g L-1 | 10.64 | [48] | | 5 | Mixed tea waste | pH of 2, adsorbent dose of 2 g L-1, contact time of 180 minutes, temperature of 303-323 K, initial Cr(VI) concentration of 10-30 mg L-1, and agitation speed of 250 rpm | 94.34 | [49] | | 6 | Spent tea leaves | pH of 10, adsorbent dose of 2 g L-1, contact time of 60 minutes, and initial Cr(VI) concentration of 25.6 mg L-1 | 3.168 | [68] | | 7 | Spent tea leaves | pH of 3, initial Cr(VI) concentration of 50 mg L-1, adsorbent dose of 0.7625 g, and contact time of 100 min | 47.98 | [69] | | 8 | Tea waste | Contact time of 60 minutes, room temperature, initial Cr(VI) concentration of 152 ppm, and agitation speed of 100 rpm | 5.20 | [70] | | 9 | Nanoceria-loaded tea waste | pH of 3, adsorbent dose of 0.8 g, temperature of 333 K, and initial Cr(VI) concentration of 10 mg L-1 | 32.15 | [71] | | 10 | Red and black tea waste | pH of 2, temperature of 298 K, contact time of 60 minutes | 1.4-3.3 | [72] | | 11 | Green tea residue | pH of 2, adsorbent dose of 2 g L-1, contact time of 40 minutes for pu-erh, 180 minutes for tieguanyin, and 360 minutes for green tea | 6.15 | Present study | | Pu-erh residue | 19.50 | | Tieguanyin residue | 12.31 |
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