Use 'factitious' to emphasize that an action is insincere and may evoke distrust. His factitious concern for the charity was purely for public image.
Pro Tip 2/3
Negative Nuance
'Factitious' often hints at a negative judgment towards something unreal or contrived. The novel's characters felt factitious and unconvincing.
Pro Tip 3/3
Avoid Misuse
Don't confuse 'factitious' with 'factual'. 'Factitious' means artificial, not factual or real. She gave a factitious account of events, which raised suspicions.